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PROBLEM IN ELECTRICITY 











HARPER’S 

EVERY-DAY 

ELECTRICITY 

HOW TO MAKE AND USE FAMILIAR 
ELECTRICAL APPARATUS 


BY 

DON. CAMERON SHAFER 

AUTHOR OF 

‘‘harper’s BEGINNING ELECTRICITY” 

WITH MANY ILLUSTRATIONS 



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> ) ■) 


HARPER & BROTHERS PUBLISHERS 

NEW YORK AND LONDON 
MCMXIV 


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COPYRIGHT, 1914, BY HARPER ft BROTHERS 


PRINTED IN THE UNITED STATES OF AMERICA 
PUBLISHED OCTOBER. 1914 


OCT 3 1914 


©CI.A379859 

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CONTENTS 


PAGE 

INTRODUCTION .. xi 

CHAPTER I—BATTERIES AS A SOURCE OF ELECTRICITY . i 

Battery Cells Furnish Cheap Electricity—Elements of the 
Battery—The Electrolyte—Measuring Electricity—Force, 
Energy, and Power—Friction—Open-Circuit Cells—Dry- 
Cell Batteries—The Gravity Cell 

CHAPTER II—DETAILS OF BATTERY CIRCUITS .... 14 

Series-Parallel Connection 

CHAPTER III—CONTROLLING BATTERY CIRCUITS . . 19 

0 

The Double-Pole Switch—Directing the Current—For Open 
Circuits—Importance of the Fuse—The Electric Buzzer— 

The Electric Bell 

CHAPTER IV—BUZZER SIGNAL SYSTEMS AND BURGLAR- 
ALARMS . 30 

A Complete Buzzer Signal System—Installing the Electric 
Door-Bell—Burglar-Alarms—Other Battery Signal Sys¬ 
tems—For the Refrigerator—Fire-Alarms—Door-Alarm 

CHAPTER V—ELECTRIC BATTERIES FOR LIGHTING PUR¬ 
POSES .43 

Miniature Lamps—Lighting the Dark-Room—White and Red 
Lights—Lighting Dark Closets—Lighting the Attic—Elec¬ 
tric Lights for the Motor-Boat—The Handy Flash-Light— 
Series Lighting on the House Circuit 

CHAPTER VI—THE STORAGE BATTERY AND ITS USES . 54 

Non-Lead Storage Batteries—Various Uses of the Storage 

Battery—The Action of the Battery—Resistance of Storage 

Batteries—Making an Experimental Storage Battery 

• • 

Vll 









CONTENTS 


PAGE 


CHAPTER VII—PRODUCING AND DISTRIBUTING ELECTRI¬ 
CAL ENERGY.66 

Loss in Producing Electricity from Steam—Where the 
Energy of the Coal is Lost—Distributing Electricity about 


the City—Lighting the Streets—Measuring the Current 

CHAPTER VIII—ELECTRIC CIRCUITS AND HOW THEY ARE 
INSTALLED. 75 

The Two-Wire Circuit—The Three-Wire Circuit—The Con¬ 
ducting-Wires—Allowable Carrying-Capacities of Copper 
Wires, and Other Data—Resistances Per Mil-Foot 

CHAPTER IX—INDOOR WIRING SYSTEMS.84 


Molding Work—Knob and Tube Work—Protecting the 
Wires with Pipe—Armored Cable Wiring—Service Wires— 
Installing the Fuse—Branch Circuits—Symbols, Tables, Etc., 
Pertaining to House Wiring 

CHAPTER X—CONTROLLING THE ELECTRIC CURRENT . 9 7 

Adding to the Comfort of Electric Light—Wall-Switches— 
Placing the Switch— Two and Three Way Switches—The 
Master Switch—Insulators 

CHAPTER XI—THE USE AND MISUSE OF LIGHT .... 109 

Light-Streamers—Measuring Light—Light is Easily Absorbed 
—The Spectrum—Color Values—Increase of Illumination 
for Various Colored Wall-Coverings—Placing the Lamps— 

How to Figure Cost of Light—Calculating Illumination— 
Correcting the Light in the Kitchen—Lighting the China- 
Closet—Lighting the Cellar—Electricity for the Bedroom 
—Illuminating the Rest of the New Home 

CHAPTER XII—THE INCANDESCENT LAMP AND ITS ADAP¬ 
TATIONS .128 

Light Caused by Resistance—Experimenting with the In¬ 
candescent Lamp—Adaptations of the Incandescent Lamp— 
Illuminated House Number—Drop-Light for the Work- 
Bench—Suitable Lamp-Shades—Lamps for the Shaving- 
Mirror—Lighting the Pantry Shelves—The “Trouble” 

Lamp— A Dual-Purpose Lamp—Desk-Lamps—Lighting the 
Piano—Decorative Use of Miniature Lamps 

CHAPTER XIII—RESISTANCE, AND HOW IT CHANGES ELEC¬ 
TRICITY TO HEAT.. 

Specific Resistance of Metallic Wires 

• • • 

VUl 







CONTENTS 

PAGE 

CHAPTER XIV—ELECTRIC HEATING-DEVICES AND HOW 
THEY ARE MADE.156 

Toy Electric Incubator—Electric Soldering-Iron—The 
Electric Cigar-Lighter—Heating the Shaving-Mug— An 
Electric Toaster—The Electric Radiator 

CHAPTER XV—GENERATING ELECTRICITY BY MECHANI¬ 
CAL POWER.169 

Electromagnetic Induction—Inducing an Electric Current— 
Different Kinds of Generators 

CHAPTER XVI—CONSTRUCTION DETAILS OF A SMALL 
GENERATOR.181 

Making a Magnet—Building a Generator—Adjusting the 
Electromagnet—Frames of Cast Iron—Making the Armature 
—Winding the Armature—The Commutator — Exciting the 
Field-Coils—Power for the Small Generator—Alternating- 
Current Generators 

CHAPTER XVII—THE DIFFERENCE BETWEEN DIRECT AND 


ALTERNATING CURRENT.191 

CHAPTER XVIII—MEASURING ELECTRICITY.196 

The Ammeter—The Voltmeter—The Watt-Hour Meter 

CHAPTER XIX—TRANSFORMING ELECTRICAL ENERGY 
INTO MECHANICAL ENERGY.205 


Direct-Current Motors—Alternating-Current Motors— 
Power Applications in the Home—Electric Fans—The Kit¬ 
chen Motor—Installing Electric Power 

CHAPTER XX—HELPS FOR THE SMALL MOTOR-BUILDER . 218 

Making the Armature—Mounting the Armature— A Larger 
Motor—Another Type of Armature—Assembling the Motor 
—Generators Can be Used as Motors 

CHAPTER XXI—THE INDUCTION-COIL AND THE OPERA¬ 
TION OF THE TRANSFORMER.229 

The Transformer—The Value of the Transformer 

CHAPTER XXII—SMALL TRANSFORMERS FOR HOUSEHOLD 

CIRCUITS.239 

Making a Resistance-Box—Details of Transformer Con¬ 
struction—Building Small Transformers— A Core-Type 
Step-Down Transformer—Connecting the Coils 

CHAPTER XXIII—A SMALL ELECTRIC PLANT FOR THE 

COUNTRY HOME.246 

Essentials of the Private Plant—Uses of Electricity in 
the Farm Home—Electric Light for the Farm-House— 


IX 












CONTENTS 


PAGE 


Electric Motors for the Home—Size of Motors to Use on 
Different Household Machines—Electric Motors for Farm 
Power—Size of Motors to Use on the Different Farm Ma¬ 
chines—Righting Wrong Impressions—The Power of Water 
—How to Make a Weir— The Horse-Power of the Wind— The 
Gasolene-Engine 

CHAPTER XXIV—INSTALLING A SMALL ELECTRIC PLANT . 

A Small Windmill-Plant—Details of a Water-Power Plant— 
Electric Lights from the Gasolene-Engine—The Storage 
Battery—The Generator—Controlling the Current—The 
Lamp Circuit—Reducing Cost to Actual Figures—Cost of 
Operation— A Standard Voltage Plant 


260 


GLOSSARY OF TECHNICAL TERMS 
INDEX ... . 


271 

279 




INTRODUCTION 


I T is important that every one should have a common 
working knowledge of electricity. Only a few of us 
can hope to become electrical engineers, but there is no 
reason why we should not all possess a certain understanding 
of this source of energy. Indeed, some knowledge of the 
subject would seem absolutely necessary now that elec¬ 
tricity is used generally for lighting the home, for power at 
the factory, for operating the automobile, for cooking 
purposes, for driving street-cars, ringing door-bells, for 
telephone and telegraph systems, and a hundred and one 
other every-day purposes. 

Electricity is a form of energy. It is useless to try to 
explain it. Neither is it necessary to ponder over the 
various accepted theories pertaining to its origin. We 
know how it behaves under ordinary conditions. This 
knowledge, meager enough, is quite sufficient for all prac¬ 
tical purposes. We know that electricity flows readily 
upon good conductors, such as copper wire. We can 
measure this flow, its pressure or voltage, can tell exactly 
the resistance in its path, and figure the amount of work 
it will do. And so it is no matter if we cannot see elec¬ 
tricity, if we do not know exactly how and why this form 
of power, or energy, exists. Those of us who use electricity 
in so many forms are interested only in results. 

Electricity traveling along a copper wire behaves exactly 
like a stream of water flowing through a pipe so far as 

xi 




INTRODUCTION 


actual results are concerned. Electricity flows in the form 
of an invisible current over the wire. This current rushes 
along at the terrific speed of more than 185,000 miles a 
second. The volume of this current may be increased 
or decreased at will; its pressure may be raised or lowered; 
it will produce energy, or horse-power, in exact relation to 
the volume and its pressure just as a stream of water will 
produce horse-power. Because electricity is invisible and 
the flow of current is expressed in amperes instead of gallons 
or cubic feet, the pressure in ..volts instead of pounds to the 
square inch, the power in watts instead of horse-power, it is 
hard to understand. Once these simple terms are mastered 
it is easy to understand the 'flow of electricity over a 
copper circuit. 

Boys are always interested in things electrical. They 
have an inherent desire to know how things are accom¬ 
plished, to learn how everything is made. Combined with 
this is the desire to do things, to build, to construct, to 
keep hands and mind busy at the same time. It is the 
purpose of this book to describe and make plain all electrical 
apparatus in common use. Through these pages the youth¬ 
ful reader will also find detailed descriptions and plans for 
making a great many interesting and useful experimental 
electrical devices. 

Incorporated herein is a simple explanation of the funda¬ 
mentals of every-day electricity. 1 The story of electricity 
is told in few and simple words, from the power-house, where 
it is manufactured, to the wires which carry it underground 
and through the air to our homes and offices, factories and 
mills, m.nes and railroads, where it is readily changed into 
light, heat, and mechanical power. Each chapter contains 

1 For a full explanation of elementary electricity and its appliances see Beginning 
Electricity, by Don Cameron Shafer, Harper & Brothers, publishers, 

xii 


INTRODUCTION 


various examples and experiments, amply illustrated with 
line-drawings and half-tone cuts to demonstrate all im¬ 
portant points. A large number of electrical toys, interest¬ 
ing experiments, and practical devices, such as any boy can 
build, are also fully described and illustrated in detail. 

The best way to learn how and why the electric motor 
produces power is to build a small motor. This is equally 
true of all electrical apparatus. It is not difficult to con¬ 
struct toy motors. Indeed, any boy with a working knowl¬ 
edge of electricity can easily build a small motor large 
enough to be operated from the lighting circuit. In order 
to repair or make any changes or extensions in an ordinary 
household lighting circuit it is absolutely necessary for the 
amateur to know exactly what he is doing. He must be 
perfectly familiar with good wiring practice; must know 
the value of insulators, the position and location of switches, 
fuses, cut-outs, and outlets which are the part of every 
electrical circuit. Without this knowledge it is dangerous 
to make repairs or changes to household wiring. Properly 
installed electricity is safer in the house than any other 
form of energy for heat, power, and light. It cannot ex¬ 
plode; it gives off no dangerous fumes and gases. If it 
is installed as it should be there is no danger of fire. 

If we must have electric lights, electric ranges, and cook¬ 
ing-devices in the kitchen and dining-room and electric 
motors for power it is necessary to know how to care for 
the various circuits, how to install these devices in the home. 

The new metal-filament miniature lamp made electric 
lighting from batteries a success. A number of serviceable 
and inexpensive applications of battery-lighting are de¬ 
scribed in this book. Battery-lighting has also been 
extended to the automobile, the motor-boat, etc. 

It is important that the home lighting system be correctly 


xm 


INTRODUCTION 


installed, so that no light is wasted, so the rays are properly 
reflected, so the eyes are protected. In Every-day Electricity 
this is amply explained and illustrated. Electric heating and 
cooking devices are new to most of us. Those who desire to 
use them should fully understand their construction and 
their limitations. No less a person than Thomas A. Edison 
has said that the future of electricity means the application 
of electrical energy to all moving things. This is still 
the morning of electricity, and the boys of to-day will 
need to know a great deal about this form of energy in their 
future lives. 

Don Cameron Shafer. 


HARPER’S EVERY-DAY ELECTRICITY 











































































































HARPER’S 

EVERY-DAY ELECTRICITY 


Chapter I 

BATTERIES AS A SOURCE OF ELECTRICITY 

E lectricity is secured from two sources. 

By far the greater portion is produced by magnetic 
generators, or dynamos. These generators are driven by 
various sources of mechanical power. Some are driven by 
steam-turbines, others by gasolene-engines, water-wheels, etc. 
They produce electricity in large quantities at low cost. 

Less than one per cent, of our electrical energy is secured 
from chemical batteries. This is because batteries are cum¬ 
bersome and costly where a heavy current is desired. 

When only a small amount of electricity is required the 
battery, or chemical generator, is best and cheapest. In 
the galvanic cell the energy resulting from certain chemical 
changes takes the form of electricity. This current may be 
used for various purposes. 

Energy changes its form hundreds of times. Doubtless it 
exists in many ways of which we have no knowledge. 
It may lie dormant for centuries, as in the form of coal. It 
may be stored in the form of certain materials, only to 
reappear when these substances are consumed by chemical 










HARPER’S EVERY-DAY ELECTRICITY 


action. When the metal zinc is destroyed by sulphuric acid 
chemical energy is released and changed into electrical 
energy. The destruction of the zinc is a form of combustion. 
It is very similar to the consumption of coal by fire. 

There are two classes of batteries used in electrical work. 
The galvanic, or primary , battery actually produces a 
current of electricity. The storage, or secondary , battery 
merely stores or, more properly, accumulates electric 
energy in the form of chemical energy. A battery, as the 
name implies, is composed of two or more galvanic cells. 
In every-day talk we frequently hear a single cell called a 
“ battery.” 

Battery Cells Furnish Cheap Electricity 

Beyond a doubt battery cells furnish the cheapest, safest, 
and best means of studying electricity. They lend them¬ 
selves easily to electrical experiments of all kinds. They 
can be used over and over again for various purposes until 
actually worn out. They offer an unlimited opportunity 
for electrical experiment and for the development of new 
and novel applications of electricity. Batteries for actual 
service can be purchased cheaper and better than they can 
be made. All the pioneers of the greater electrical industry 
used galvanic cells as a source of current in their experi¬ 
mental work. Indeed, it was not until about forty years ago 
that the magnetic generator was perfected. 

A simple primary battery cell consists of four essential 
parts. The first is the container , usually a glass or porcelain 
jar. This merely serves to hold the liquid contents of the 
cell. The second is the liquid itself, which is termed the 
electrolyte. The plates, called electrodes , are usually of zinc 
and copper or zinc and carbon. The zinc plate is slowly 
consumed by the electrolyte. This chemical action pro- 


BATTERIES AS A SOURCE OF ELECTRICITY 

duces a flow of electrical energy. The electricity is taken 
from the battery plates by leading -wires which complete the 
necessary external circuit. Electricity produced in this 
way does not difler from that produced by direct-current 
magnetic generators. It may be used for various purposes, 
such as lighting small lamps, running small motors, ringing 
door-bells, operating buzzers, etc. 

Just how the chemical action of the electrolyte on the 
plates produces a flow of electricity is hard to explain. 
The oxidation of the zinc is really a slow-burning process. 
The zinc is gradually eaten away until it disappears entirely. 
The copper or carbon element is not seriously affected by 
the chemical action. It really is not of serious consequence 
how this current of electricity is produced. We are more 
interested in results than theories. 

Battery cells have but two serious defects. It is quite 
impracticable to obtain pure metals for the plates. This 
results in local action , or chemical activity even when the 
external circuit is broken, so the plates gradually waste 
away. Amalgamating the zinc plate with a thin coating of 
mercury remedies this to a certain extent. The negative 
plate of the cell becomes covered with tiny particles of 
hydrogen gas which increases the internal resistance of the 
cell until it ceases to produce a flow of electricity. It is 
then said to be polarized. Means must be provided to 
eliminate this hydrogen. This is accomplished by adding 
certain chemicals to the cell which unite with the hydrogen 
before it collects on the negative electrode. These chemicals 
are known as depolarizing agents. 

When the sulphuric-acid solution in Fig. I begins to act 
upon the zinc it tears the metal apart, changing it into 
zinc sulphide. It also liberates hydrogen gas which col¬ 
lects on the surface of the copper plate. This action is 

3 



HARPER’S EVERY-DAY ELECTRICITY 


accompanied by a flow of electricity from the poles and 
wires of the external circuit back to the zinc. 

The electromotive force (abbreviated E. M. F.) of this 
battery cell is about 1.02 volts. The current produced 

by the cell is nearly steady 
and continues to flow as long 
as both the internal and out¬ 
er circuits are closed. If 
either is opened the chemical 
■ action ceases, and of course 
the electricity stops. The 
chemical action cannot take 
place unless a path, or cir¬ 
cuit, is provided for the flow 
of what electricity is pro¬ 
duced. 



Elements of the Battery 

The E. M. F. of a battery 
cell is always in direct pro¬ 
portion to the extent of the 
chemical action on the pos¬ 
itive element. By a series of tests it has been found that 
the following materials are arranged in accordance with 
their voltage-producing qualities: 


1. Aluminum 

2. Zinc 
3- Tin 

4. Cadmium 

5. Lead 

6. Antimony 

7. Bismuth 

8. German silver 

9. Brass 
10, Mercury 


11. Iron 

12. Steel 

13. Copper 

14. Silver 

15. Gold 

16. Carbon 

17. Platinum 

18. Iron sulphide 

19. Manganese dioxide 

20. Lead peroxide 


4 

























































































BATTERIES AS A SOURCE OF ELECTRICITY 


Any of these elements in the list may be taken as positive. 
I hose below it in the list will be negative to it. The 
farther apart they are in the list the greater will be the 
voltage of the cell. In a practical battery, however, only 
those elements can be used which are inexpensive and 
best adapted for the work in hand. For instance, aluminum 
and gold would make a good battery, but few could afford 
to use it. Aluminum and lead peroxide would be difficult 
to handle. Zinc and carbon are cheap, easy to handle, and 
make the best battery for ordinary purposes. 


The Electrolyte 


Different solutions are used for different batteries. 
Among the various compounds used for the electrolyte 
are the following: 


Caustic potash 
Caustic soda 
Ammonia 
Sulphuric acid 
Nitric acid 
Hydrochloric acid 
Iron chloride 


Silver nitrate 

Biuestone, or copper sulphate 
Zinc sulphate 
Ferrous sulphate 
Potassium iodide 

Ammonium chloride, sal ammoniac 
Common salt 


In the internal circuit of the battery cell the electrical 
current flows from the positive, zinc, to the negative, carbon, 
element. In the external circuit, however, this order is 
reversed, and the electricity flows from the carbon, which 
is now termed the positive pole, to the zinc, or negative 
pole. Thus it will be seen, by referring again to Fig. i, 
that the current travels over a complete, or circuitous, 


course. 

Primary batteries are roughly divided into two classes, 
depending upon the service for which they are to be used. 
For continuous service, where a steady flow of current is 

5 


HARPER’S EVERY-DAY ELECTRICITY 

required at all times, the closed-circuit battery must be used. 
This type of battery is peculiarly adapted for such work. 
Its plates will not easily polarize and destroy its power. 



F« 3 . 2 


Neither will it wear out quickly. For intermittent service 
the open-circuit battery is best. Such batteries produce 
a good flow of current at a greater pressure. But they soon 
polarize and wear out. If allowed to rest the depolarizing 
agent performs its offices, and the cell is ready for more work. 

Illustration (Fig. 2) shows types of primary batteries with 
caustic-soda cells, the sides of the cells being cut away or 
made transparent to show plates. In Fig. 3, A shows carbon 
and zinc cells, B two fluid cells, and C zinc and copper gravity 
cell. 

Measuring Electricity 

Here it may be well to take a leaf from Beginning Elec¬ 
tricity , also published by Harper & Brothers, and explain 
just how electricity is measured. Following are the units 
used for measuring electricity, with their common equivalents 
given by way of explanation: 

0 










BATTERIES AS A SOURCE OF ELECTRICITY 


ELECTRICITY 

Volt 

Potential 

Electromotive force 

Ampere 

Watt ' 

Kilowatt (i,oco watts) 

Resistance 

Ohm 


WATER 

Pressure 

Pressure 

Pressure 

Current, or rate of flow 

Fraction of horse-power 

One and one-third horse-power 

Friction 

Friction 



Fig. 3 


An ampere is the current resulting from one volt pushing 
its way over a resistance of one ohm. 

Amperes X volts = watts 
Watts -r-746 = horse-power 
Volts -r-amperes = ohms 

Force, Energy, and Power 

Force is a pressure expressed in a push or a pull. Energy 
is the ability to do work. It is divided into potential energy 
and kinetic energy. 


7 
























HARPER’S EVERY-DAY ELECTRICITY 


Potential energy is the ability of a body to perform work at 
any time when it is set free to do so. 

Kinetic energy is the ability of a moving body to do work 
during the time its motion is being arrested. 

Work is overcoming resistance through space. In the 
English system of weights and measures the common unit is 
the foot-pound. 

Power is the rate of doing work. Work is an expression 
entirely independent of time, but power always takes time 
into consideration. For instance, to lift one pound one 
foot is one foot-pound of work, no matter in what time it is 
done, but it takes sixty times as much power to do it in one 
second as it would take to do it in one minute. 

Friction 

The resistance which a body meets with from the surface 
on which it moves is called friction. It is called sliding- 
friction when one body slides on another; for instance, a 
sleigh is pulled along on ice—the friction between the 
runners of the sleigh and the ice is sliding-friction. It is 
said to be rolling-friction when one body is rolling on another 
so that new surfaces continually are coming into contact; 
for instance, when a wagon is pulled along a road the 
friction between the wheels and the road is rolling-friction, 
but the friction between the wheels and their axles is sliding- 
friction. Sliding-friction varies greatly between different 
materials, as everybody knows from daily observation. 
For instance, a sleigh with iron runners can be pulled 
with less effort on ice than sand, even if the road is ever so 
smooth. This is because the friction between the iron and 
ice is a great deal less than the friction between iron and 
sand. 


8 


BATTERIES AS A SOURCE OF ELECTRICITY 


Closed-Circuit Cells 

The closed-circuit cells in common use, named after 
the men who perfected them, are given in the following 
table: 


NAME 

+ PLATE 

ELECTROLYTE 

DEPOLARIZER 

— PLATE 

E.M.F. 

R. 

Daniell 

Zinc 

Sulphuric acid 

Copper sulphate 

Copper 

I - OS 

I 

Grove 

Zinc 

Sulphuric acid 

Nitric acid 

Platinum 

1.9 

•IS 

Bunsen 

Zinc 

Sulphuric acid 

Nitric acid 

Carbon 

1.8 

• 2 

Paggendorff 

Zinc 

Sulphuric acid 

Bichromate of 







potassium-sul¬ 
phate acid 

Carbon 

2 

. 2 

Lande 

Zinc 

Caustic potash 

Copper oxide 

Iron 

1 

. I 

Davy 

Zinc 

Ammonium 






chloride 

Silver chloride 

Silver 

1.1 

4-5 


The last column in the above table gives the approximate 
values of the internal resistance of these cells in ohms. 
This includes the resistance of the plates as well as that 
of the liquids. 

Open-Circuit Cells 

Cells with weak depolarizers recuperate very quickly and 
are suitable for open circuits. The common types used for 
this work are as follows: 


NAME 

+PLATE 

ELECTROLYTE 

DEPOLARIZER 

— PLATE 

E. M. F. 

R. 

Leclanche 

Zinc 

Sol. of sal am- 

Binoxide of 

Carbon 

1.48 




moniac 

manganese 

•s 

Law 

Zinc 

Sol. of sal am- 






moniac 

None 

Carbon 

1.37 

•4 

Gassner 

Zinc 

Oxide of zinc, 
sal ammoniac, 
chloride of 







zinc, plaster 

None 

Carbon 

i -3 

. 2 


Dry-Cell Batteries 

Dry-cell batteries are most extensively used for open- 
circuit service, d hey are easily transported and handled. 

9 



































HARPER’S EVERY-DAY ELECTRICITY 


There is no danger of spilling the exciting liquid. The 
elements cannot be easily disarranged. The dry cell is 
made up of about the same materials as the wet cell, except 
the electrolyte and the depolarizer are in paste form, inclosed 

in a tight metallic cup. 
Dry cells cannot be 
readily renewed. They 
are inexpensive and 
are generally used in 
modern battery equip¬ 
ments (Fig. 4). 

In the dry cell the 
zinc tube, or positive 
element, also serves 
as the protective con¬ 
tainer of the cell. The 
other elements are 
placed inside the tube 
and surrounded by a paste-like chemical mixture, made up 
as follows: 

1 part sal ammoniac 1 part granulated carbon 

1 part chloride of zinc 3 parts plaster 

1 part peroxide of manganese 1 part flour 

2 parts water 

The top of the tube is sealed with insulating-compound, 
and the terminals brought out to the binding-posts for 
connection. The E. M. F. of this cell equals 1.5 volts* and the 
internal resistance is about .3 ohm. 

Dry cells are best for experimental work, as they give 
out no dangerous gases. There is no acid or corroding 
liquids to spill out and destroy things. They can be easily 
and simply connected to various electrical devices. On 
account of their small cost they can be thrown away when 


CONNECTING 



IO 

















BATTERIES AS A SOURCE OF ELECTRICITY 

exhausted. 1 hey should be kept in a dry place so that 
the cardboard container will not get damp and corrode the 
zinc tubes. Care must be taken not to crack or injure the 
sealing-compound at the top of the cell or it will dry out and 
become useless. Cells that are more than a year old, even 
if they have not been extensively used, should be thrown 
away. Old cells rapidly deteriorate and are practically 
worthless. Where only a few battery cells are connected 
up together they can be placed in a bunch. Where many 
of them are connected in series to produce a higher voltage 
they must be kept apart in wooden containers. 


The Gravity Cell 

Closed-circuit batteries, for continuous service, are 
seldom used except for telegraph-lines, railroad-signals, and 
burglar-alarms. These cells produce a continuous flow 
of current. They are not suitable for open-circuit work. 
A simple closed-circuit cell can be made of a strip of zinc 
and a strip of copper immersed in a salt solution in a glass 
jar. Such a cell is useless, except for experimental pur¬ 
poses, as the copper soon polarizes and stops the flow of 
current. 

The gravity cell is generally used lor closed-circuit work. 
The plates are copper and zinc. The zinc is in the form of a 
casting, known as a crow’s-foot because of its shape. It is 
made with a protruding lip which fastens to the top of the 
glass jar and keeps the zinc near the top of the solution. 
The copper consists of three strips riveted together in a star- 
shape. This is placed on edge in the bottom of the jar. 
It is provided with a rubber-insulated copper wire long 
enough to reach to the top of the jar, where it forms the 
positive terminal. It is insulated to prevent the wire from 




HARPER’S EVERY-DAY ELECTRICITY 


coming into contact with the zinc and forming a short 
circuit and to prevent chemical action on the wire (Fig. 5). 

The electrolyte is composed of rain-water and blue vitriol. 
About three pounds of the crystals are placed about the 
copper plate and the jar filled with water. The zinc element 
should be suspended about four inches above the copper 
element. The water should be sufficient to cover the zinc. 
If the cell is short-circuited for a few hours the electrolytic 
action will form zinc sulphate about the zinc element and 



copper sulphate about the copper. Quick action is secured 
by adding a small amount of sulphuric acid or common salt. 

If there is none of the sulphate solution or sulphuric acid 
added when the cell is first set up it should be short-circuited. 
That is, it should be connected between the copper and 
zinc terminals with a piece of wire for one or two days to 
form sulphate of zinc and at the same time lower the internal 
resistance. They should be kept in a room where the tempera¬ 
ture is 70° to 85° or 90° Fahrenheit. The internal resistance, 
which is normally two or three ohms, increases very rapidly 


12 













































































































BATTERIES AS A SOURCE OF ELECTRICITY 


with a drop in temperature below this point, 70°. For this 
reason they should be kept in a warm place, as heat promotes 
chemical action upon which the cell depends for its opera¬ 
tion. The blue line marking the boundary between the 
blue copper-sulphate solution in the bottom of the cell and 
the colorless zinc-sulphate solution in the top of the cell 
should be about half-way between the copper and zinc 
elements. These solutions remain separate on account of 
their different specific gravities or densities, the colorless 
zinc sulphate being lighter in weight for the same volume. 
It is from this fact that the cell derives its name —gravity 
cell. If the blue line marking the boundary between the two 
solutions is above this point some of the blue solution, or 
copper sulphate, can be siphoned off, or the cell may be 
short-circuited to form more of the zinc sulphate or colorless 
solution. When the blue line is too low more of the blue- 
stone, or copper-sulphate crystals, and water should be 
added. 







Chapter II 


DETAILS OF BATTERY CIRCUITS 

T HE electromotive force of a battery cell is the moving 
force. It causes the flow of current over the wires of 
the circuit. 

This electromotive force, usually abbreviated E. M. F., 
is really the pressure, or voltage , between the terminals of the 
battery. It is measured and expressed in volts. 

The electromotive force of a cell is not influenced by the 
size of the battery plates. The voltage of a small cell is 
exactly the same as the voltage of a large cell. Only the 
volume of the current is increased by enlarging the plates. 
The E. M. F. of a zinc-copper-sulphuric-acid cell is about 
one volt; that of a zinc-copper-sal-ammoniac cell one and 
one-half volts. The best batteries give only about two volts. 

If batteries are to be used for various purposes it is quite 
necessary to know just how much electricity each cell will 
produce. Knowing the capacity of a single cell, it is easy 
to figure out the proper number of cells for all circuits. 

It is not difficult to determine the capacity of a battery 
cell. They are usually rated in ampere-hours. An ampere- 
hour really means an ampere of current flowing for one hour. 
This is best illustrated by a simple example. A cell gives 
.5 ampere for 30 days continuously. The total number of 
hours it was in service is 30x24, or 720 hours. Divided by 
the ampere capacity of the cell, .5, equals 360 ampere-hours. 

14 


DETAILS OF BATTERY CIRCUITS 


If this same cell was used intermittently for but io minutes 
each hour of the day, then it would last approximately 180 
days. Ten minutes each day multiplied by 24 hours 
equals 240 minutes, or a total of four hours a day. If the 
ampere-hour capacity of the battery is 360 ampere-hours, then 
the cell will last in this service for 36o-^(4x.5), or 180 days. 

An ampere-hour is one ampere used for one hour. 

A half ampere used for two hours is equal to one ampere- 
hour. A half ampere used two minutes out of each hour 
for sixty hours is also equal to an ampere-hour. 

The amount of current delivered by a cell depends upon 
the E. M. F. of the cell and the resistance of the circuit. 
This current is always equal to the E. M. F., which is ex¬ 
pressed in volts, divided by the total resistance of both the 
external and internal circuits. Example: 


Volts 

Resistance 


= current 


A cell of two volts and an internal resistance of one ohm 
will send .66 ampere of current through a two-ohm wire. 


2 volts-^(i ohm+2 ohms) = .66 ampere 


Remember that the total resistance of the circuit is the 
resistance of the external circuit added to the resistance of 
the internal circuit (Fig. 1). 

If we have a buzzer line which will not work from a single 
cell with an E. M. F. of 1.5 volts owing to an excess of 
external resistance, we can easily add another cell in series 
and raise the pressure to three volts, or still another, raising 
it to 4.5 volts, and so on (Fig. 2). 

i-S + I -S+ I -S=4-S voIt s 

The positive pole of one cell is connected to the negative 
pole of the next, and so on. The poles of the end cells are 

15 











HARPER’S EVERY-DAY ELECTRICITY 

used as the terminals of the battery. A battery connected 
in series is shown in Fig. 3. 

In this case the total E. M. F. of the battery equals the 
sum of the electromotive forces of each cell, since the external 
potential of the end cell is made up by adding the potential 
difference between the poles of the individual cells. 

Take, for example, 10 cells, each having a voltage of one 
volt, with an internal resistance of. 025 ohm and an ampere- 


EXTERNAL CIRCUIT 



Circui-fc 



1.5T + 1.5 + 1.5=4.5volis 


Fig. 2 


% 



BATTERY + 



GEL.L. 


Fig. 3 


Fig. 4 


hour capacity equal to 200. If they are connected in series 
the total voltage would be 10 x 1, or 10 volts, an internal 
resistance of 10 x.025, or .25 ohm, but the capacity is only 
200 ampere-hours. 

When a large current at low voltage is desired the cells 
are connected in parallel (Fig. 4). 

The total ampere-hours available from cells connected in 
parallel is equal to the sum of the ampere-hour capacities 
of the cells so connected. The voltage is equal to that of 

16 


















































































DETAILS OF BATTERY CIRCUITS 

the single cell. The internal resistance is equal to that of a 
single cell divided by the number of cells in multiple. 

Connected in this way, the six cells are equal to one 
cell with plates six times as large as the single cell. The 
voltage remains the same as in a single cell. 

If two cells each of one-volt and 200-ampere-hour capacity 
are connected in multiple the ampere-hour capacity will be 
doubled, but the voltage will remain the same. 

Series-Parallel Connection 

In some instances to obtain the maximum amount of 
current with a given number of cells it is advisable to use a 
combination of both methods described above. The cells 
are connected in separate series groups, and these groups 
are connected in parallel. Fig. 5 illustrates such a con¬ 
nection. 

The total voltage is determined by the number of cells con¬ 
nected in series and the ampere-hour capacity by the number of 
sets of cells in multiple. 

In Fig. 5 these are shown five in series and six in multiple. 
If we use the same type of cells as described above—one- 



2 17 

































































HARPER’S EVERY-DAY ELECTRICITY 


volt, 200 ampere-hour, and .025-ohm internal resistance— 
then the voltage available would be five, the ampere-hours 
6x200, or 1,200. The internal resistance of an individual 
cell divided by the number of cells in multiple, or .025 
divided by 6, and multiplied by the number of cells in 
series, which is 5, or (.025-7- 6) x 5 = .0208 ohm. 

These conditions above mentioned are determined by the 
laws of divided circuits. 

By inserting in the battery circuit a switch with several 
points of contact it is possible to get a wide range of varia¬ 
tions in the voltage and the current of such a set. The 
simplest type of such a controlling device is illustrated in 
Fig. 6. 

With this simple switch it is possible to readily connect 
two, three, four, five, or six batteries in series by merely 
manipulating the switch-arm to the various positions. 
This switch is of the greatest value in experimental work. 
With it a wide range of voltage can be secured. 


1 


Chapter III 

CONTROLLING BATTERY CIRCUITS 

E lectricity likes to choose its own path. It wastes 

no time in wandering about. It always takes the easiest 
way home. 

But regardless of distance it must always travel over a 
conductor. 

The electric wire is the path over which electricity travels. 
To keep it on this path the wire, or conductor, must be 
insulated with non-conductors. 

All metals are good conductors of electricity. Water, 
most liquids, the earth, and various other materials are 
fairly good conductors. 

Air is the best non-conductor. It requires 20,000 volts 
or more of electricity to jump across one inch of air space. 
Rubber, glass, and porcelain are also good non-conductors. 

The paths, or circuits, over which electricity travels are 
often as complicated as the city streets over which we travel. 
But electricity cannot be trusted to find its own way. It 
must be directed—sent. It must be under absolute control. 

Electricity is controlled with switches. These are small 
devices to make and break the circuit, or to direct it over 
various paths or lines. 

There are hundreds of types of electric switches. New 
ones are made every day. In fact, every amateur can devise 
and make his own switches. 


19 




HARPER’S EVERY-DAY ELECTRICITY 


The essentials of a good switch are an insulated form, or 
base, brass or copper contacts, and a suitable insulated 
handle, key, or button. 

There are four kinds of line - switches in common use. 
They are the single-pole switch , the double-pole switch , the 
triple-pole switch , and the four-pole switch. 

A single-pole knife-blade switch is generally used to open 
and close continuous circuits. It is made of brass or cop¬ 
per strips and provided with an insulated handle. In 
fact, this handle is not necessary for low voltage, and the 
brass strip may be bent into handle form (Fig. i). 

The block is three by five inches, and an inch thick. The 
brass or copper blade is drilled or punched at one end for 
riveting to the binding-post and an insulating handle 
fitted to the other end. The binding-post is bent so the side 
arms are springy enough to make a good connection to the 
blade when the switch is closed. 

All metal contact-points should be clean and well polished , as 
a coating of rust or dirt acts as an insulator. 

The completed switch is merely inserted in the line. 
Raising or lowering the handle breaks and makes the circuit. 

The Double-Pole Switch 

The double-pole switch is used where it is necessary to 
open and close both the positive and negative legs of the 
circuit. It is merely a double single-pole switch (Fig. 2). 

The double-pole switch can be easily made. A glance at 
the diagram given in Fig. 2 will show the entire construction 
better than a detailed explanation. The dimensions de¬ 
pend entirely upon where it is to be used. 

The triple-pole switch is used only for three-wire circuits. 
This switch is seldom necessary for amateur work. It is 

20 


CONTROLLING BATTERY CIRCUITS 



Fig. 1 




Fig. 2 




Fig. 3 


merely a combination of the single-pole switch and the 
double-pole switch (Fig. 3). 

Battery circuits are generally low-voltage circuits; there¬ 
fore hard, dry wood is ample insulation for such switch¬ 
boards, bases, and handles. Care should be taken, however, 


21 









HARPER’S EVERY-DAY ELECTRICITY 


to keep the wood dry. If exposed to moisture it should 
be well oiled or varnished. Oil and varnish are good 
insulating materials and will keep the moisture out. 

If the voltage is raised above ten volts dry wood should not 
be used , and hard rubber or porcelain should be substituted. 

The success of all low-voltage electrical circuits depends 
upon good insulation and perfect connections at all joints, 
splices, and contact-points. Care should be taken in the 
manufacture and installation of all controlling devices. 

Knobs and handles for low-voltage switches can be 
turned on a small lathe (Fig. 4). 

After the knob is turned a hole is drilled through the 
center and countersunk for the screw. When the screw 
is in place the space above the screw-head is filled with 
melted sealing-wax, flush with the wood, effectively fasten¬ 
ing the screw in place and insulating the metal from the 
hand. 

Knobs and handles can also be molded of sealing-wax 
and hard rubber. Both sealing-wax and hard rubber 
become soft and plastic under the influence of heat. A 
plaster-of-Paris mold is suitable where the wax is used. 
Do not try to work soft rubber. 

The mold for hard-rubber insulators is made of wood in 
two halves. It should be warmed in an oven before the 
hard rubber, made soft and wax-like by heat, is placed within 
the halves. It should then be squeezed in a vise. 

Directing the Current 

To direct the current over various paths a different type 
of switch is necessary. 

Where it is necessary to switch the current from one 
circuit to another a directing-switch is used. A very good 

22 


CONTROLLING BATTERY CIRCUITS 


switch of this kind can be easily made of a brass strip and 
a few empty brass cartridge-shells (Fig. 5). 

The baseboard A is six inches square. As many holes 
are bored as there are circuits. These holes could be 
arranged in a circular form and the right size to hold the 
cartridge tightly. The brass strip B is connected to the 
binding-post by a single screw so it will swing easily. It is 




Fig. 5 




2 ? 


jBrass sirij6 B 



Car-fnctge^ 


Fig. 6 


bent, as shown in the illustration, so as to make a firm 
contact with the brass heads of the cartridges and provided 
with a wooden insulating-handle. The leads of the different 
circuits are connected to the individual cartridge through 
holes punched through the sides of the brass shell (Fig. 6). 


For Open Circuits 

For open circuits these switches, as described above, will 
not do at all. A push-button or a spring switch is necessary 
for this work. These au¬ 
tomatically keep the line 
open to protect the bat¬ 
tery. Otherwise the open- 
circuit battery would soon 
run down and cease to 
produce electricity. 

The best of all these 
spring devices, for low- 

voltage circuits, is the ordinary push-button (Fig. 7). 

23 




































HARPER’S EVERY-DAY ELECTRICITY 


It is evident that pressure on the insulated button A will 
bring the two metallic parts B, B in contact to which the 
two lead-wires C, C are connected and thus close the circuit. 

This type of push-button is only suitable for battery work 
where the voltage is not above 75 volts. Its carrying capacity 
is limited to a fraction of an ampere. 

The importance of making good joints and contacts 
should be remembered. For all permanent work such 
contact-joints, at switches and otherwise, should be soldered. 
This insures a perfect connection and an uninterrupted flow 
of the low-voltage battery current. For temporary work 
care should be taken to make good clean contacts. Often 
the failure of an electrical experiment is due to make¬ 
shift joints which act as barriers to the current. It re¬ 
quires more than 20,000 volts of electricity to leap across 
one inch of air space. A little figuring will show just how 
tiny an air space will stop the flow of a four-volt circuit. 
A few grains of dirt, a film of oil are quite sufficient. 

Importance of the Fuse 

Battery-current wires should be properly fused where 
they leave or enter a building. This precaution will prevent 
dangerous stray currents from accidentally entering the 
building over the telephone, telegraph, wireless, or buzzer 
circuit wires. If the electric-light wires or power-transmission 
wires should blow down and fall across your telephone or 
telegraph lines , if lightning should strike the poles , a dangerous 
current might easily enter your home and injure any one near 
the instrument or set fire to the house. 

This is reason enough why every amateur electric line 
should be amply protected where it enters the house with a 
suitable fuse placed in the circuit. 

24 


CONTROLLING BATTERY CIRCUITS 


A fuse is merely a device for inserting a bit of lead-com¬ 
position wire in the circuit. There are various types of 
fuses (Fig. 8). 

It will be noted from Fig. 8 that the fuse designed for 
telephone lines is merely held in clips on a suitable insulating- 
block, while the fuse designed for house-lighting circuits is 
screwed into a socket the same as an incandescent lamp. 



-Leacf 

Wire^ 


Coob&ch 
v 


^— C o t) t a c t- 

wi 


bead 


wrre- 


^<Cor)ta 


rass 


cmtra 

.. i irh in 

_j _ sbeii 

\ Coni.&ct w iib 

v ~r insulated- ' 


X Grlass to.fee- 


ci 


House fuse 


Fuse-box, 
fuse, and 
switch 

Fig. 8 


Wooden cabinet with 
distribution switches, 
fuses, etc. 


These fuses work on the selfsame principle. The bit of 
lead-composition wire is designed to carry a certain amount 
of electricity and no more. Any attempt to overload them 
with current above the stipulated amount will melt the lead 
wire and thus automatically open the circuit. 

Fuses can be bought cheaper than they can be made. 
They cost but a few cents each. When burned out by an 

25 















HARPER’S EVERY-DAY ELECTRICITY 


excess of current they should be thrown away. Never 
attempt to repair a fuse. 

Fuses also protect the telephone instruments , buzzers, lamps , 
and other electrical devices from excessive and dangerous 
currents. Delicate instruments and costly devices might 
easily be ruined in an instant by stray currents if not properly 
protected with fuses. 

The Electric Buzzer 

The simplest of all battery devices is the electric buzzer. 
Simple as it is, it has a hundred uses. The buzzer is adapt¬ 
able for signaling, for simple telephone lines, for call-bells, 
for annunciators and alarms, etc. 

The buzzer is merely an electromagnet and a vibrator so 
combined as to produce a loud buzzing whenever the circuit 
is closed. Of course the buzz is produced by the rapid 
vibrating of the armature in front of the electromagnet as 
it makes and breaks the circuit. 

The buzzer is really a little sound-motor. It is a device 
which turns the electrical energy into mechanical energy, 

like every other motor. 
This mechanical energy is 
used to set up sound¬ 
waves in the surrounding 
D air which produces the 
buzz. The very simplest 
form of buzzer is shown 
in Fig. 9. 

An electromagnet of 
four ohms resistance is made by winding cotton-cov¬ 
ered No. 36 wire on an ordinary carriage - bolt. This 
magnet is affixed to the wooden base, which acts as an 
insulator, as shown in the above picture. Above it is 

26 


































CONTROLLING BATTERY CIRCUITS 

stretched a short piece of steel piano-wire three inches 
long, between the binding-posts D, D. The tension is regu¬ 
lated by the screw C. At the top of the wooden post D 
is mounted the brass arm F, which holds the regulating- 
screw G. On the steel wire opposite the screw G is fast¬ 
ened a bit of platinum, silver, or even iron which is bent 
in the form of a tube and flattened down tight against 
the wire so it will stay in place. One battery lead is 
connected to the binding-post E and the other to the 
post H, to which are also connected the leads to the 
magnet. 

The operation of the buzzer is very simple. When the 
current is sent through the electromagnet it attracts the 
steel wire, pulling it down and away from the screw G. 
This breaks the circuit, instantly the magnetism ceases, and 
the wire snaps back against the contact, closing the cir¬ 
cuit. This operation is repeated as long as the circuit is 
closed. The steel wire vibrates at high speed, and this 
produces the buzzing noise. 

Another simple buzzer is made on this same principle 
by simply bending a piece of steel clock-spring over the 
electromagnet in place of the piano-wire. The end of the 
spring is heated to draw the temper and drilled so it can 
be fastened at one end to the baseboard. It is mounted 
the same as the wire (Fig. io). 

Buzzers are made for operation on regular lighting-circuits 
where the voltage is no or 120 volts. But those described 
above are only suitable for operation on low-voltage circuits. 
Any attempt to place them in lighting-circuits will result 
in failure and the destruction of the buzzer. A buzzer 
for a lighting-circuit can be purchased [cheaper than it 
can be made. They are generally used for signaling pur¬ 
poses. 


27 




HARPER’S EVERY-DAY ELECTRICITY 


The Electric Bell 


The electric bell is but an adaptation of the buzzer prin¬ 
ciple (Fig. n). 

The clapper A is fixed to the end of the armature B. 
The vibration of this armature manipulates the clapper 
against the bell whenever the push-button is pressed, 
closing the circuit. 

The little button on the door-jamb is a spring device 
which keeps the circuit open between the battery and the 






3 


3 


.Not 


-C 


,WoV 



A [" Yoke- _. 

' '-cj-'Nup Detail o/ . 

coipstroctiorj. 

Fig. 12 


bell. The pressure of a finger closes the circuit, and the 
electricity flashes over the line to the bell. The bell itself 
is somewhat more intricate than it looks. In the little iron 
box beneath the bell are two small coils of fine insulated 
wire wrapped tightly about the soft-iron cores. Of course 
when electricity flows through the insulated wire of these 
coils the soft-iron cores become electromagnets, differing 

28 






















































CONTROLLING BATTERY CIRCUITS 


from a permanent magnet in that when no electricity flows 
through them, owing to any break in the circuit, they are 
not magnetic. 

When the button is pushed, closing the circuit, these 
magnets attract a soft-iron plate, or armature, attached to 
the lower end of the bell clapper and located just in front of 
the magnetic poles. This iron plate is fastened at one end 
to a steel spring, but the coils are powerful enough when 
magnetized to overcome the action of this spring and to 
pull the plate downward. This action pulls the clapper 
down against the bell, and at a certain point just before the 
armature touches the magnet the electric current is broken, 
destroying the pulling-force of the magnets, and the steel 
spring throws the clapper back. Of course the circuit is 
then closed again and the action is repeated as long as the 
button is pushed. 

Electromagnets for buzzer and bell service are best made 
in three parts (Fig. 12). 

The soft-iron yoke A is drilled to admit the two small 
iron bolts B, B. The bolts are wrapped with two layers of 
stiff writing-paper, fitted with wooden or cardboard disks 
(C, C) and wound in the usual manner with fine insulated 
copper wire. The result is a very powerful electromagnet of 
compact size. 

Details of such battery devices as the telegraph, the 
telephone, electromagnets, induction-coils, toy motors, etc., 
are given in full, with illustrations, in Beginning Electricity , 
the first of this series. 


Chapter IV 


BUZZER SIGNAL SYSTEMS AND BURGLAR-ALARMS 

B UZZER SIGNAL systems are very easily installed. 

They really save many steps. This is especially true 
of country districts. For instance, suppose the barn is some 
little distance from the house. It is frequently necessary 
for some one to go there to call the head of the house or the 
farm-hand. All these steps and many others could be 
saved by installing a cheap and handy buzzer call-system. 

A buzzer system of this kind requires but a common 
buzzer, a push-button, a couple of dry-cell batteries (the 
actual number of cells depending, of course, on the dis¬ 
tance), and the necessary wire. The ordinary low-voltage 
electromagnet buzzer mentioned in the preceding chapter 
will answer very well indeed. Otherwise, low-voltage buzz¬ 
ers can be purchased for a few cents each. Any ordinary 
wire can be used, and it need not be insulated for outdoor 
lines. If iron wire is used it should be of the size commonly 
known as telephone wire. Copper wire may be smaller, as 
it is a better conductor of the electric current. 

One good dry cell will be sufficient to operate lines up to 
one hundred yards, and an extra cell should be added for 
every additional fifty yards'. This rule will not always 
hold, owing to the imperfections in the line or poor batteries. 
Enough cells should be placed in series until the buzzer 
operates at its best. 


30 


BUZZER SIGNAL AND B U R G L A R - A L A R M S 


Wh ere the line enters the building insulated wire should be 
spliced to the uncovered outdoor wire. Silk or cotton 
covered wire will do for indoor work if it is properly rein¬ 
forced with porcelain or rubber tubes where it passes 
through the walls. Outdoors the naked wire should be 
insulated at ail points of suspension and where it touches 
such objects as buildings, trees, walls, etc. Buildings and 
wood of all kinds will short-circuit the line during damp 
weather. Common glass insulators will answer for out¬ 
door work. In the absence of these bottle-necks may be 
used. The bottle-necks can be knocked off and fitted to the 
end of a wooden holder. Broken glass is sharp—handle it 
with gloves and care. The holders are nailed to the build- 




Bofile yeck 
iQScila^er wfjere. 
wire ^orQS 
sfjort .corner. 


ings, fence-posts, trees, etc., and fitted with bottle-necks to 
hold the wires (Fig. i). 

It is a regrettable fact that boys frequently become so 
enthusiastic in experimental work of this kind that they 

3i 







































HARPER’S EVERY-DAY ELECTRICITY 


neglect the most important details. In their haste to get 
the work done they do not take sufficient pains with little 
things. And it is these very little things which mark the 
difference between success and failure. Be sure to make 
all wire connections tight and firm. Be sure to scrape the 


Li 9 


e- 


k> 

kb 1 

35 er - 


Tosb Bottom 


£>u 


3 o 


.Ql 




Pu5^Boti0Q., 


er y 


BUZZER SIGNAL LINE 

Fig. 2 


metal clean and bright when splicing wires. Be sure that 
binding-posts make a good connection to circuit wires. 
And be doubly sure that the electric wires are carefully 
insulated for their entire length against any possible short 
circuits. Remember to insert a fuse in the line where it 
enters each building. 


A Complete Buzzer Signal System 

With these little details firmly in mind it is no trick at all 
to install a buzzer signal line. It should be used only for 
short-distance work. For greater distances a telephone or 
telegraph is better. By following the diagram given above 
the buzzers and batteries can be easily connected so they 
will work (Fig. 2). 

A simple set of signals can be agreed upon for the buzzer 

32 











BUZZER SIGNAL AND BURGLAR-ALARMS 



ALTERNATING-CURRENT BUZZER AND COMBINED SNAP-SWITCH AND BUZZER 


line. When such a line is built between the workshops of 
neighboring boys it is but natural that they should learn to 
talk over the wires by using a telegraph code (Fig. 3). In 
this case a short buzz 
stands for a dot and a 
long buzz for a dash. 

Where the line is built 
to connect the house 
with the barn or with the 
chicken - plant or shop 
a simple code of sig¬ 
nals will answer. 

-One long ring, 

‘‘Dinner is ready.” 

- - - Three short 
rings, “Some one to see 
you. 

Two long rings,“You are 
wanted at the house.” 

- - - - Four short 
rings for horse and 
buggy. 

This may be enlarged 
at will to take in a great 


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ABBREVIATED NUMERALS USED BY CONTINENTAL OPERATORS. 

m 2« • ■» S — 

• »»• 9 » • IO 

WIRELESS ABBREVIATIONS 

•4 - PLEASE START ME,WHERE 
13 - UNDERSTAND 
23-AM BUSY NOW 
30-NO MORE 
*73-BEST REGARDS 
77-MESSAGE FOR YOU 
92- DELIVERED 
99-KEEP OUT 
-DISTPESS SIGNALS* 

MORSE. _C.Q.D. CONTINENTAL. 


G. E.- 
G. N.- 
G.M.- 
G. A.- 
O.S.- 
D. M.- 
M.S.G.- 
O.P.R.- 


GOOD EVENING 
*. NIGHT 
« MORNING 
GO AHEAD 
SHIP REPORT 
FREE MESSAGE 
•MESSAGE 
•OPERATOR 


S.O.S. 


33 


Fig. 3 



































































































































































HARPER’S EVERY-DAY ELECTRICITY 


variety of signals. It is surprising how many steps a system 
of this kind will save. 

It is also easy enough to attach a simple telephone to this 
buzzer system. In this case the buzzers are used merely for 
calling the party to the telephone, then the conversation is 
carried on over the wire. This can be very easily done by 

attaching a simple tel¬ 
ephone - transmission 
receiver across the line 
at each station (Fig. 

4) . 

It is a well-known 
fact that the tele¬ 
phone transmitter can 
be used as a receiver for short distances. In this case 
the instrument is held first to the lips and applied to the 
ear as soon as your part of the conversation is finished to 
catch what the other party answers. To operate you 
merely press the push-button, which operates the buzzer 
at the other end of the line. When the party answers 
with a short buzz you talk by means of the receiver. The 
manner of connecting the receivers to the line is shown 
in Fig. 5. 

In case the distance is so great that a battery and induction 
coil are necessary for the successful operation of the telephone 
they should be connected up as shown in Fig. 6. 

Installing the Electric Door-Bell 

A single dry-battery cell will operate the electric door-bell 
in any ordinary home. For convenience' sake the bell 
should be placed in the back of the hall or in the kitchen, 
where it will be sure to be heard. Any small-size silk or 
cotton covered wire may be used. 

34 


















BUZZER SIGNAL AND B U R G L A R - A L A R M S 


Remember that such a circuit calls for a double length 
of wire. There must be enough to reach from the front 
door to the bell and back again to complete the circuit. 
The push-button is fastened in a conspicuous place beside 
the front door. A bronze metal-covered button is best for 
such outdoor service, as it looks better and lasts longer. 
The wires are concealed as much as possible by running them 
down along the door-jamb, along the mop-boards, or under 
the floor. It is the general practice to carry the wires 
straight down to the cellar, where the battery is connected 
on. The wires are then fastened to the floor joists and 



Receiver-Bei* . 

Fig. 5 





Fig. 6 


beams to a point just below the bell, where they are carried 
up through the floor to the bell (Pig. 7)* 

It will be seen that the circuit is kept open by the push¬ 
button. The pressure of a finger closes the circuit and 
rings the bell. 


35 



































HARPER’S EVERY-DAY ELECTRICITY 


Burglar-Alarms 

Burglar-alarms are in general use in both city and country. 
They are very inexpensive and can be easdy installed by 
the amateur. Such alarms can be constructed to guard the 
doors and windows of the store or shop. They can be 
easily applied to the chicken-house, the barn, or pigeon-loft. 
They are also used to protect the home. 

A burglar-alarm consists of a battery, the necessary wires 
and switches, and a suitable gong or bell which rings when 
the burglar tries to enter. 

The only alarm worth considering is the closed-circuit 
system. In this system the alarm is not sounded by making 
an electrical connection, but by breaking it. This system 
absolutely defies the burglar, as any tampering with the 
wires, either in the buildings or with the internal system 
including the line itself, instantly sounds the alarm. Of 
course electric bells can be used in place of buzzers. If the 
object is to catch the miscreant a good loud buzzer is better. 
It makes less noise. A loud-toned bell is pretty apt to 
frighten away the would-be burglar. 

The closed-circuit system is so installed that if the line is 
opened at any point, or the wires are cut or broken in any 
manner, the buzzers sound the alarm. For the man who 
lives near his store or office this system is a great conve¬ 
nience. It is also suitable for the farmer who desires to 
protect his chicken-coop, pigeon-loft, woodshed, stable, 
barns, etc. The best thing about this system is the fact 
that the wires do not have to be concealed. They may 
be exposed to view. If the burglar should cut the wire 
the bell would ring immediately and announce his unwel¬ 
come visit. 


36 


BUZZER SIGNAL AND B U R G L A R - A L A R M S 

The closed-circuit alarm system necessitates a buzzer 
or bell, a dry battery, an electromagnet, and a gravity bat¬ 
tery such as is used for closed-circuit telegraphy work. The 
apparatus is arranged as in Fig. 8. 

In the sketch, A is a pivot on which turns the armature, 
so fixed that when pushed toward the magnets it will 



Fig. 9 

make connection at B. The electromagnet will hold it 
there until the closed circuit is broken. Then the spring 
will pull it against C, making the contact to ring the bell. 
After the connection has once been broken it cannot be 
pulled back except by pushing the arm in some mechanical 
way. D is a switch to turn the bell off during the time the 
alarm is not wanted. All connections are explained in the 
sketch. 

Connections are made at the various windows by arrang¬ 
ing a copper washer on the bottom of the sash and one on 

37 

































HARPER’S EVERY-DAY ELECTRICITY 

the sill so that they make a good contact when the window 
is closed and break it the instant the window is raised. 
Door connections are made at the jamb so that the con¬ 
nection is broken when the door is opened. 

The dry battery is used on the bell side of the system and 
the gravity batteries in the relay side. 

At best the foregoing is but a suggestion of what may be 
done in the way of installing burglar-alarms. Working on 
the same principle as the closed-circuit relay system de¬ 
scribed above, the device may be installed to suit any 
condition and for any purpose where such an alarm is 
necessary. It is even possible and practical to guard fruit- 
trees with this system. In this case a very fine wire is so 
arranged that it incloses the trees and must be broken in 
order to reach the fruit. It may be so concealed that it is 
accidentally broken by the nocturnal visitor. It is easy 
enough to protect the chicken-house with such a system or 
any other barn building. A convenient switch turns off the 
entire system while the owner does the necessary work 
about the buildings. 

There are places, however, where the closed-circuit 
burglar-alarm is best. This system is simplest of all, but 
the circuit wires must be concealed, because if they are 
cut or broken the alarm is rendered useless. Only the 
guarding-wires of this system may be exposed to view, as 
the cutting or breaking of this wire at any point will sound 
the alarm (Fig. 9). 

An intermediate wire keeps the bell short-circuited, and 
the moment this wire is broken the bell rings and continues 
until the switch is turned off. This wire should be placed 
across the doorway so when the door is pushed open it will 
break the wire; or it may be put at any place where you are 
sure the intruder will break it. 

38 


BUZZER SIGNAL AND B U R G L A R - A L A R M S 


Other Battery Signal Systems 


Battery signal systems are also useful for various other 
purposes. Where the water for the home is stored in a 
tank, being raised by a pump whenever the tank is empty, 
a simple system may be installed to sound a warning 
when the water in the tank gets low, or to automatically 
start and stop the electric motor and pump. Both these 
systems are shown in Fig. io. 

The operation of this signal system is very simple. When 
the float drops to a certain low level it completes the elec- 


Li^e 



_- v .-' 

1/ Bu^er 
i5 desjred- 


trical connection, and the buzzer sounds the alarm or the 
motor starts the pump. The buzzer may be located in any 
place desired, but it is usually installed in the kitchen. 
When it sounds its alarm the hand-pump or gasolene-engine 
is started up and the tank refilled. Where an electric motor 

39 






































• HARPER’S EVERY-DAY ELECTRICITY 

is used to drive the pump an alarm is not necessary. Of 
course, dry batteries are always used for open-circuit work 
of this type. 

For the Refrigerator 

This same signal system is easily adapted to the water- 
pan under the refrigerator. These water-pans seem to be 
always running over on the floor. A buzzer system will give 
ample warning when the pan is full and should be emptied 

(Fig. n). 

Perhaps the operation of this device is best shown in the 
picture. When the float rises to the top of the pan it 
closes the circuit and sounds the buzzer alarm. 

Fire-Alarms 

Automatic fire-alarms are also operated by battery cur¬ 
rents. The little telltale device which announces the 
presence of the fire and sounds the alarm is called a ther¬ 
mostat. A thermostat sufficient for this purpose can be 
made by riveting a strip of hard rubber securely to one 
side of a strip of clock-spring (Fig. 12). 

When heated the steel expands, but the rubber contracts. 
Consequently the contracting rubber causes the steel spring 
to buckle or bend. Advantage of this is taken so that the 
buckling spring closes an electrical circuit which rings the 
alarm (Fig. 13). 

These thermostats are usually located where fires are apt 
to break out. For instance, a farmer-boy arranged one in 
the incubator and brooder house. When one of the ma¬ 
chines became overheated and caught fire the electric bell 
located in the house sounded the alarm, and the building and 
contents were saved. 


40 


BUZZER SIGNAL AND B U R G L A R - A L A R M S 


In this case a thermostat was located directly over the in¬ 
cubator and one over each brooder. The wires were ex¬ 
tended to the house, where the electric bell was fastened to 
the wall of the room near the boy’s bed. 

A metal thermostat is made of a strip of brass brazed to a 
strip of steel. It acts similar to the steel-rubber combina¬ 
tion. There are many modifications of this fire-alarm sys¬ 
tem. Some of the larger buildings employ fusible plugs 
which melt with very little extra heat and thus automatically 




open the circuit and sound the alarm through a relay 
and bell. These types are suitable for large buildings 
only. 

There is still another good fire-alarm device which is 
easily made. It works on the same principle as the fuse. A 
bit of sealing-wax is used to break the circuit. When this 
wax melts the circuit is completed and the alarm sounds 
(Fig. 14). 

It requires but a little heat to melt out the intervening 

4i 




































HARPER’S EVERY-DAY ELECTRICITY 



Xirj® 



sealing-wax. Then the steel spring snaps down on the 
conductor terminal and completes the circuit so the alarm 
rings. 

Door-Alarm 


It is often very convenient, especially in workshops and 
offices, to know just when the door is opened. A simple 
battery alarm is easily adjusted to any door (Fig. 15). 

When the door is opened the lower spring-contact is 
forced up and against the upper contact, completing the 
circuit and ringing the bell. 





























































Chapter V 


ELECTRIC BATTERIES FOR LIGHTING PURPOSES 

B ATTERIES are also used for lighting purposes. Either 
primary or storage batteries may be used for lighting 
circuits, although their original cost and short life makes 
this method too expensive for extensive operations. 

Many of the electric-light stations throughout the country 
maintain large storage batteries as an emergency source of 
power. In case anything happens to the engines, generators, 
or other machinery the service wires are switched to the 
battery, which carries the load until repairs can be made. 

Household lighting circuits are generally of at least no 
volts. This high voltage is maintained as standard for 
several important reasons. The cost for copper wire 
increases in proportion to the drop of voltage. There is a 
considerable loss of energy where a low-voltage current is 
carried for any distance. It is at once apparent that to 
attain this standard voltage with batteries would require 
nearly a hundred battery cells, connected in series, other¬ 
wise the no-volt lamps would not light. But incandescent 
lamps are also made in low voltages. With the advent of 
the new metal - filament lamps a few years ago electric 
lighting from batteries was made less expensive. For the 
first time it came into general use, especially on motor-boats 
and automobdes. These new lamps will give a candle- 
power of light for every watt of energy consumed, or about 

43 





HARPER’S EVERY-DAY ELECTRICITY 

a third of the current required for the old miniature lamp. 
Miniature lamps (Fig. i) are now made in very low voltages, 
according to the following table: 


MINIATURE LAMPS 


CANDLE-POWER 

VOLTS 

WATTS 

AMPERES 

Flash-lights 

2.7-6.2 


•35 

A 

i-5 

. 6 

.40 

I 

2.8 

.84 

•3 

i J A 

3-8 

I 14 

•3 

2 

6.2 

i. 86 

•3 

4 

4-6 

5 

1-25 

4-5-6 

6-8 

0 

— 

1 

L/~> 

•95-1-25 

8-10-12 

6-8 

10-20 

2.1-3-35 


Knowing the voltage and the amperes required for each 
miniature lamp, it is easy enough to determine the battery 
cells necessary for any lighting circuit of this nature. Sup¬ 
pose we desire to install a two-candle-power four-volt lamp 
to be operated by dry cells. If each cell gives 1.5 volts, 
then three of these cells connected in series will produce 
4.5 volts. Theoretically this is half a volt too much, but in 
practice it is well to allow at least that much. The ampere- 
hour capacity of the cells is 50. If the lamp requires yi 
of an ampere the cells will keep the lamp burning for 100 
hours. 

Lighting the Dark-Room 

Battery lighting with low-voltage lamps is quite exten¬ 
sively used in the dark-room, where photographic plates 
and films are developed. Such a lamp is very easily in¬ 
stalled. The lamp itself costs but a few cents and can be 
purchased with a red bulb. A two-candle-power four-volt 
lamp will answer this purpose very well. This lamp can be 

44 















ELECTRIC BATTERIES FOR LIGHTING 

operated with three dry cells. Use good insulated wire 
No. 16 for the circuits, carefully protected with porcelain 
cleats at all points of contact. Ordinary lamp-cord con¬ 
taining two insulated wires may be safely used and stapled 





Fig. 1 



to the walls, if care is taken not to cut the insulation when 
the staples are placed. The lamp is usually suspended so 
the light will fall where needed, and the batteries are placed 
under the bench or table out of the way. The current is 
controlled with a common snap-switch or a home-made 
knife-blade switch (Fig. 2). 

In case the lamp is not provided with a red bulb it 

45 


























HARPER’S EVERY-DAY ELECTRICITY 


should be provided with a red shade or screen. The lamp 
can be mounted in a small wooden box, placed on a handy 
pedestal, with one side of the box removed and a piece of 
stiff red paper substituted (Fig. 3). 

The wooden pedestal is 12 inches high, the wooden shade 
is 6 inches square. The lamp is turned on or off with a 
pull-socket such as used on ordinary electric-lamp sockets. 
This lamp has the added advantage that the little door is 
hinged so it can be raised when a white light is wanted. 

White and Red Lights 

A dark-room is generally all its name implies, and often 
both a white light and a red light are necessary. While 
getting materials together, making repairs, or cleaning up, 
the white light, of larger candle-power, is used. When de¬ 
veloping, this lamp is switched out and the red lamp lighted. 
In this case a suitable six-pole snap-switch is necessary for 
controlling the lamp (Fig. 4). 

Lighting Dark Closets 

Almost every house has a dark closet or two, a dark 
stairway, or a dark store-room. Lights are needed in these 
rooms even on the lightest day. It is extremely dangerous 
to enter them with a lighted lamp or a candle, or to strike 
matches while searching in the darkest corners. These 
dark closets prevail even in modern houses equipped with 
electric light, and they are all too frequent in old houses. 

The only safe light for a dark closet stored with highly 
inflammable material, as they always are, is an electric 
light. Such a closet can be easily and economically lighted 
with a low-voltage lamp and a common battery circuit. A 

46 


ELECTRIC BATTERIES FOR LIGHTING 




single two-candle-power four-volt lamp suspended from the 
ceding will give ample light. The current is secured from 
three dry cells placed behind the door, out of the way, or on 
the far end of a convenient shelf. A snap-switch placed 
near the entrance makes it convenient to turn the light 
on and off before entering the room. The manner of wiring 
depends, of course, on the size and nature of the room, but 
should be, in general, similar to the system shown in Fig. 5. 


Lighting the Attic 


In this list should also be included attic lighting. A great 
many fires start from carelessly held lamps or carelessly 

47 









































































HARPER’S EVERY-DAY ELECTRICITY 

dropped matches while folk are searching the attic after 
dark. By all means the attic should be lighted with elec¬ 
tricity. Attic lighting is more extensive than the examples 
given above and will require more batteries, larger wires, 
and at least two miniature lamps. 

The lights in a dark attic are seldom used, and then only 
for a short interval, so they can be of larger candle-power, 
to illuminate a larger area. Two four-candle-power six-volt 
lamps will give plenty of light. This will require five 
1.5-volt cells connected in series, and perhaps six if the 
wiring is very extensive (Fig. 6). 

This system can also be adapted, with such variations as 
necessary, to instal a lighting system in the cellarway or in 



the portion of the cellar where the daylight is obstructed, 
as in the vegetable-cellar. In case night work is required 
about the chicken-house, as frequently happens during the 
winter months, such a lighting system can be installed 
in the hen-house. This will eliminate all danger from 
matches, hand - lamps, or lanterns. The cost of such a 
system is very insignificant. 

Care must be taken in operating all these low-voltage battery 
lighting circuits to turn the lamps out when not in use. To 

48 











ELECTRIC BATTERIES FOR LIGHTING 


leave the lamps burning is a serious drain upon the batteries. 
When the batteries are worn out they are worthless and must be 
replaced. Make it a rule to look and be sure the lamps are 
turned out before you close the door. 

Electric Lights for the Motor-Boat 

On all public waterways motor-boats are required by law 
to carry a certain number of lamps after dark. Gasolene- 
driven boats of all kinds are easily destroyed by fire. A fire 
out in the middle of a large lake is as dangerous as it could 
well be. For this reason matches and oil-lamps are more or 
less dangerous on motor-boats. Large quantities of oil and 
gasolene are necessarily spilled about the boat, especially 
in the engine-room. For this reason electric lamps are 
safer and best for motor-boat lighting. 

Contrary to the general belief, the motor-boat can be 
lighted from electricity secured from dry batteries. Large 
boats are usually supplied with an engine-driven dynamo, 
or generator, or with a large and expensive storage battery 
for lighting and ignition purposes. These boats are brill¬ 
iantly lighted each night. But small boats require only the 
regulation sailing-lights, with, perhaps, a small light or two 
in the cabin. These boats are seldom used after dark and 
can be lighted with dry batteries just as well as not. 

For small boats, under 30 feet, a six-volt lighting system, 
similar in many ways to that installed on an automobile, is 
satisfactory in every way. As a source of current four sets 
of five cells connected in multiple-series should be installed 
in a convenient locker where they will be out of the way. 
It makes no material difference where the battery is located. 
Rubber-covered wire should be used because the wiring 
must be proof against dampness, which would cause short 
circuits, and all sorts of trouble. No. 16 rubber-covered 
4 49 


HARPER’S EVERY-DAY ELECTRICITY 


copper wire is right. In an ordinary single-cabm boat ten 
or twelve automobile lamps will be necessary, arranged as 
follows: 

Cabin, two 5 -candle-power lamps 

Engine-room, one 5 -candle-power on flexible cord 

Galley, one 2 ^-candle-power 

Steps, one 2 ^-candle-power 

Search-light, one 24 -candle-power 

Side-lights, two 5 -candle-power 

Mast-light, one 5 -candle-power 

The lamps in the galley and for the entrance to the cabin 
should be fastened to the ceiling. Side-wall brackets are 
provided for the cabin lamps, and the engine-room lamp 
is attached to a long flexible cord for trouble-hunting, etc. 
(fig- 7 )- 

The search-light is a heavy drain on the battery, but it is 
seldom used, and then only for short periods. The star¬ 
board and port lights (Fig. 8) and the mast-lights must be 
























































DRY 

CBATTERIE5 

rOOOOOl 
OGO-GG- 
“©-©-©-0O- 
GG^GG©" 


ELECTRIC BATTERIES FOR LIGHTING 

lighted after sundown on all large rivers, lakes, canals, 
etc. 

1 he method of connecting the battery and dividing the 
circuits is best shown in Fig. 9. 

The diagram shows a method of connecting batteries and 
the different circuits to 
the switchboard. The 
batteries are connected 
to a double-pole, double¬ 
throw switch. The fuses 
are of a capacity equal 
to the sum of the am¬ 
perages of all the cir- 5w,T€ r7 

cuits. Six circuits run anmj-z it - -4^ 

from the switchboard f TT 
and should be equipped ° l~H"-—(S 

with switches and fuses 
of correct capacity. Circuit- 5 

Circuits Nos. I, 4, 5, 
and 6 are all controlled 
directly from the switch¬ 
board. Circuits Nos. 2 and 3 are controlled at the switch¬ 
board and at the lights. 


fust 



<35-'' cff 

CIRCUIT- 


//(hi 




ID* 


Fuses 


ClRCuiT-3 


G 7 




Circuit- 6 

T£) ;c7 


Wiring Diagram 

Fig. 9 


The Handy Flash-Light 

A flash-light is a very handy little thing to have around the 
house. They are cheap and inexpensive and will last for a 
long time. Such a flash-light really consists of a tiny 
battery, a miniature lamp, with a suitable push-button 
switch and a short wiring circuit. This apparatus is usually 
combined in one case, making the lamp handy to carry. 
The switch keeps the circuit open until the button is pressed, 
and the lamp remains lighted as long as the button is pressed. 

5i 


































HARPER’S EVERY-DAY ELECTRICITY 


A flash-light can be made of two ordinary dry cells, a 
miniature lamp, and a simple spring switch. The cells are 
slipped into a pasteboard tube, one after the other. This 
tube should be of heavy cardboard fitting snugly about the 
cells. Or the cells may be placed side by side and wrapped 
with heavy paper. In the front of the tube (if a tube is used) 
is fitted a disk of soft wood about an inch thick. This disk 
is bored to admit the lamp-socket and the two wires from the 
cells. The cells are connected in series. One of the lead- 

wires is cut to admit 
the spring switch for 
controlling the cur¬ 
rent. The parts of 
an ordinary push¬ 
button can be used 
for this switch, or 
new ones can be de¬ 
vised. The switch 
is fastened to the inside of the tube, connected to the wires, 
and arranged so that the button proper operates through a 
hole in the tube (Fig. io). 

Series Lighting on the House Circuit 

It is a mistake to think that low-voltage lamps cannot be 
used on ordinary house-lighting circuits. True enough, a six- 
volt lamp will burn out with a flash if screwed into the lamp- 
socket on a 112-volt circuit. But nineteen six-volt lamps 
arranged in series can be used on a 112-volt circuit. The 
number of low-voltage lamps that can be safely used in 
series on a high-voltage circuit will be the number of volts 
of the house circuit divided by the rated voltage of one lamp. 
If the house voltage is 112 volts and the lamps are marked 

52 



La rn^> 






ELECTRIC BATTERIES FOR LIGHTING 


six volts the number of lamps required will be 112 -4- 6, or 19 
lamps. If you use more lamps than the proper number they 
will not light brilliantly, and if you use less they will burn 
too brightly and perhaps be destroyed. 

Series lighting with low-voltage lamps on household circuits 
is seldom employed except for special occasions. Christmas 


Fig. 11 

trees are generally lighted in this manner. The lamps are 
arranged in a “string” in series (Fig. n). 

So many fires have occurred from lighting Christmas 
trees with old-fashioned candles that miniature lamps are 
now generally used for this purpose. They are perfectly safe 
and may be used year after year. 


Chapter VI 


THE STORAGE BATTERY AND ITS USES 

T HE storage battery is closely related to the primary 
battery. Its action is about the same. The essential 
parts are very similar. In fact, a primary gravity cell can 
be used to a certain extent as a storage battery. 

The storage battery is also known as a secondary battery 
and as an accumulator. This latter name is far more correct, 
as the storage cell does not generate electricity. It accu¬ 
mulates, or stores, it. 

Now, lest we be misled in the very beginning, it is well 
to state again that the storage battery does not store 
electricity, nor even electrical energy. The battery stores 
up energy, it is true, but it is in the form of chemical energy. 
The storage battery is a voltaic cell in which a chemical 
action is first produced by an electric current passed through 
the cell from some external source. This chemical energy 
produced in this way may be allowed to lie dormant for a 
long time, but is ever ready to change back into electricity 
upon demand. 

It should be remembered that the storage battery differs 
materially from the static accumulator, or Leyden jar. The 
Leyden jar actually accumulates electrical energy. The 
storage battery accumulates chemical energy. 

There are two kinds of storage batteries—the lead battery 
and the non-lead battery. 

54 


i 



THE STORAGE BATTERY AND ITS USES 


In the lead battery the cathode, or positive plate, is made 
of lead peroxide, a hard substance of reddish-brown color. 
The anode, or negative plate, is made of spongy metallic 
lead. These plates are known as “grids.” They are im¬ 
mersed in an electrolyte of dilute sulphuric acid. 

The process of storing the electricity, in the form of 
chemical energy, by sending a current of electricity through 
the cell, is called “charging.” When the cell is producing 
current it is said to be “discharging.” 

When the cell is completely discharged both the positive 
and the negative plates are in the form of lead sulphate, and 
the electrolyte is practically reduced to water. 

When the charging current is again passed through the 
cell the lead sulphate in the negative plate loses the sulphate 
part and becomes pure spongy lead. The positive plate 
also loses its sulphate, which combines with the escaping 
oxygen gas and forms lead peroxide. In the mean time the 
water combines with the liberated sulphate, becoming dilute 
sulphuric acid. 

This chemical action takes place in the cell each time it 
is charged and discharged. 

Non-Lead Storage Batteries 

The greatest defect of the lead-and-lead storage battery 
is its weight. Lead, as we all know, is very heavy, and where 
a large number of cells have to be used to secure the proper 
voltage and a sufficient amount of electricity, the battery 
as a whole weighs considerable. 

For many years inventors were busy trying to improve the 
storage battery and reduce its weight. It was found that 
almost any good primary cell could be charged to a certain 
extent by passing a current through it. Acting on this 

55 



HARPER’S EVERY-DAY ELECTRICITY 


principle, Reynier made a secondary, or storage, cell, in 
which the negative plate was composed of zinc instead of 
lead. This cell was lighter, but it has several serious defects. 
Waddell and Entz, two well-known experimenters, con¬ 
structed cells of copper and zinc, but the electromotive 
force of the cell was very low. While their cell was light, 
it required three times as many cells for a given voltage as 
would be required if the lead cells were used. 

Thomas A. Edison reduced the weight of the storage 
battery considerably when he perfected his nickel-and-iron 
cell. In this battery the active materials are oxides of 
nickel and iron. The electrolyte is a solution of caustic 
potash in distilled water. 

Leaving out the chemical details in explaining the action 
of the Edison cell, it is sufficient to say that when the cell is 
charged oxygen is transferred from the iron to the nickel 
electrode. When the cell is discharged it is transferred back 
again. This cell weighs about half as much as a similar lead 
cell, but the average voltage of the cell is somewhat less, 
requiring a greater number of cells in series to produce the 
same line voltage. 

Various Uses of the Storage Battery 

We could not very well do without the storage battery. 
Indeed, it is of such great importance that there is a constant 
effort on the part of the scientists and electrical engineers to 
improve the efficiency of the battery, to make it lighter and 
easier to maintain. The storage battery has many uses. 
Among the most important are the following: 

To supply current for electric automobiles and trucks. 

To light gasolene-driven automobiles, to supply current for the ignition 
of gasolene-automobiles, and for the self-starting motors of such cars. 

56 


THE STORAGE BATTERY AND ITS USES 


To drive mining locomotives where it is not expedient to install trolley- 
wires in the tunnels. 

To operate street-cars on short lines where an overhead or under¬ 
ground trolley system would be too costly. 

To supply current for electrically driven launches. 

For ignition and lighting systems of gasolene motor-boats. 

For wireless telegraph systems. 

For home lighting service in connection with a private electric plant. 

As a source of reserve power for central stations in case of any accident 
or breakdown of the power-driven generators. 

For operation of remote control switches, etc. 

For fire and burglar systems. 

For long-distance telephone systems. 

For miners and watchmen’s lanterns. 

For the emergency lighting of large public buildings in case the central 
supply station should suddenly cease to produce current. 

For the lighting of passenger-trains. 


The Action of the Battery 

A simple storage-battery cell consists of plates of lead, 
insulated from each other and placed in a glass jar containing 
ddute sulphuric acid. The upper ends of the metal plates 
project above the liquid and are each provided with a 
suitable terminal for connecting purposes (Fig. i). 

This cell cannot be charged with alternating current. 
Direct current must be used. It is easily seen that the 
application of an alternating current would have a neutraliz¬ 
ing effect on the cell. Instead of flowing steadily into one 
terminal of the cell and out the other the alternating current 
would flow first in one terminal and then in the other, and the 
cell could not be charged. 

When alternating current only is available for battery¬ 
charging ways and means must be provided to change it 
into direct current. In large installation this is effected by 
the use of a machine called a rotary converter, inasmuch 
as it converts alternating current into direct current. 

57 


HARPER’S EVERY-DAY ELECTRICITY 



In rubber jar 


Jk 

In glass jar 


Fig. 1 




STORAGE CELLS 

This is really a combination of an alternating-current motor 
and a direct-current generator (Fig. 2). 

Indeed, a motor-generator set is frequently used for this 
very purpose. An alternating-current motor is connected 
on the same shaft with a direct-current generator. Thus, 
the alternating current which flows into the motor is made 
over into direct current by the generator at a trifling loss, 
due to friction, etc. (Fig. 3). 

But for smaller current the most efficient device to change 
alternating current into direct current for battery-charging 
service is the mercury-arc rectifier (Fig. 4). 

The mercury-arc rectifier has no moving parts. It is a 
small stationary device in which the rectification is brought 

58 


/ 


















THE STORAGE BATTERY AND ITS USES 


about in a glass bulb containing mercury and provided with 
three electrodes. The two upper electrodes are graphite, 
and the lower one is the mercury in the bottom of the bulb. 
The air is exhausted from the bulb. Suitable terminals are 
provided on the outside for connecting the inside electrodes 
to the circuit. Owing to a natural law the current can 
pass from either of the graphite electrodes to the mercury, 
but not in the opposite direction. By considering the 
electrodes as doors we can imagine that alternating current 



Fig. 2 


ROTARY CONVERTER 

enters the bulb from two electrodes or doors, using one door 
when approaching from one direction and the other when 
in the reversed direction. These doors only open in. There 

59 









HARPER’S EVERY-DAY ELECTRICITY 

is just one lower door opening out, so it can enter either 
door but must all flow one way in leaving the bulb. Surging 
back and forth over the line as often as sixty times a second, 
the electricity comes to the rectifier as alternating current 



Fig. 3 


MOTOR-GENERATOR SET 

and leaves it as direct current, with only a trifling loss in the 
transmission. 

The capacity of the rectifier is not very great. So far the 
device is only used extensively for small work, such as charg¬ 
ing storage batteries for automobiles, telephone exchanges, 
and telegraph offices. It is also used to furnish direct current 
for arc-lamps used in moving-picture lanterns and for running 
small direct-current motors from alternating-current circuits. 

Resistance of Storage Batteries 

The battery cell offers considerable internal resistance to 
the passage of the charging current. The plates are also 

60 








Fig. 4 

Front View Back View 

SINGLE-PHASE MERCURY-ARC RECTIFIER FOR CHARCING SIGNAL BATTERIES 













HARPER’S EVERY-DAY ELECTRICITY 


subject to an action similar to polarization in a primary cell. 
For these reasons in charging a storage battery a larger 
voltage is required than the cell is capable of producing on 
discharge. 

The storage battery will not give back as much electrical 
energy as was put in it. It is not ioo per cent, efficient, 
owing to a heat loss, loss through internal resistance, etc. 

Making an Experimental Storage Battery 

To understand the operation of a storage battery and to 
provide another very interesting experiment it is well to 
make a small cell. The size of the cell decides the quantity 
of current it will deliver. The number of cells, in series, 
determines the strength, or voltage. A rough estimate of one 
ampere of current for each 20 square inches of positive plate 
surface, counting both sides, will approximate the amount of 
current a cell will produce. Each cell will give a pressure, 
or potential, of about two volts. No matter what the size 
of the cell, it will deliver but two volts’ pressure. In order 
to procure a higher voltage a sufficient number of cells 
must be connected in series. 

A good experimental cell can be made in a common 
drinking-glass, using two lead plates. From a piece of 
sheet lead one-eighth of an inch thick cut two rectangular 
plates. These plates should be just large enough to slip in 
the glass at a distance of about an inch apart. They 
should not touch the bottom of the glass. A strip of hard 
wood, dry and of fine grain, one inch square and long 
enough to reach well across the top of the glass, should be 
well soaked in hot wax. Either beeswax or paraffin may be 
used (Fig. s). 

The lead plates must now be fastened to either side of the 

62 


THE STORAGE BATTERY AND ITS USES 

wooden cross-piece. Punch or bore small holes through the 
top of each lead strip and screw firmly in place. Use small 
screws, and be sure they do not meet through the wood and 



s'. 

/ 

O Wood- 0 

-—FI-Fl_ 

/ 


Fig. 5 


thus short-circuit the cell. It is best to punch the holes in 
different parts of the plates so as to be sure the screws will 
not touch when assembled. 

For terminals a small lug can be left on top of each plate 
when they are cut, or a copper 
wire can be wound around one of 
the screws, between the lead and 
the wood, just before the screw 
is fastened in place (Fig. 6). 

Care should be taken to scrape 
both the copper wire and the lead 
plate to form a good connection. 

The wire terminals should be 
short, so as to reduce external re¬ 
sistance. 

The electrolyte for this battery 
is a mixture of acid and water. 

Use one part of pure sulphuric 
acid to four parts of water. It 

63 



Fig. 6 




































HARPER’S EVERY-DAY ELECTRICITY 


is best to do this by measure. Find out how many table¬ 
spoonfuls of water the tumbler wdl hold. 11 it holds ten, 
then the mixture should contain two of acid to eight ol 
water. 

Never pour the water into the acid. Pour the acid slowly 
into the water. This will avoid the sputtering and bubbling 
which would result if the water was poured into the acid. 
Flying acid will burn the flesh and destroy clothing. Take 
no chances with it, and do not pour the water into the acid. 

But pouring acid into water causes considerable heat, and 
unless it is done very slowly this heat may break the glass. 
It is better to mix the electrolyte in a crockery jar or earthen¬ 
ware basin and pour it into the glass when it has become cool. 

This miniature storage battery may be charged with four 
dry-battery cells connected in series-multiple so as to give a 
good flow of current at about three volts. The cell should be 
given a long charge the first time. It will work better when 
it has been charged and discharged several times. 

It is very interesting to watch the action of this cell while 
it is being charged and discharged. Owing to the glass 
container every change of the battery plates can be noted. 

When a current of electricity is run into this cell the water 
is decomposed into its two component gases—hydrogen and 
oxygen. The oxygen is liberated at the positive plate (the 
one at which the current enters), and hydrogen forms at the 
negative plate (the one by which the current leaves the cell). 
The oxygen acts on the positive plate and converts its sur¬ 
face into peroxide of lead. The negative plate suffers no 
chemical change, but merely has its surface rendered soft 
and porous. This alteration of the plates continues so long 
as the charging current is applied, within certain limits, 
of course, for each cell has its limit of capacity. 

The positive plate soon becomes dark chocolate-brown in 

64 



THE STORAGE BATTERY AND ITS USES 


color, caused by the change of its surface into peroxide of 
lead, which is nearly black. The negative plate assumes a 
velvety-gray appearance—its surface merely having changed 
into spongy lead. If the charging current be now discon¬ 
nected and the plates in the cell connected by a wire a reversal 
of the process of charging will occur. The peroxide of lead 
will now gradually return to ordinary metallic lead, and while 
this change is taking place a current of electricity will flow 
through the wire from the brown positive to the gray negative. 

A lead storage battery of this kind, made in a two-quart 
glass jar, using larger plates, can be charged directly from 
the lighting circuit if it is direct current. Any attempt to 



APPARATUS USED 

1 Reversible Switch; ^ 110-Volt Lamps; 1 Bell; 2 Lead Plates; 
1 Jar with Dilute Acid; Wire for Connections. 

Fig. 7 

charge a battery with alternating current will fail. Connect 
the battery to the direct-current line as shown in Fig. 7. 

Open the switch to the bell and cut in on the direct-current 
line. The lamp, used as resistance, will burn brightly. The 
acid solution will boil; soon the positive plate will turn 
brown. Now cut out the current, and open switch to bell, 
and it will ring, showing that the battery is charged. 

5 65 
















































Chapter VII 


PRODUCING AND DISTRIBUTING ELECTRICAL ENERGY 

E LECTRICITY such as lights our homes and drives our 
street-cars and factories is produced in large power¬ 
houses. 

The generators, or dynamos, in such power-houses are 
driven by engines or water-wheels. Where water-power is 
available the energy of the falling water can be changed 
into electricity very cheaply. Where water-power cannot be 
used steam-engines are employed to drive the generators. 

The interior of a modern steam-driven electrical plant is a 
wonderful place. The old reciprocating engine has been 
relegated to the past, and the powerful steam-turbine engine 
has taken its place. You will see no huge, throbbing pistons 
sliding in their oiled sockets; no whirring, flapping belts, 
no purring dynamos. True enough, you will see all of these 
things in power-stations budt years ago, but in those being 
installed to-day these things are conspicuous by their 
absence. Instead, the powerful turbine steam-engine and 
the rotating part of the electric generator are mounted on 
the same shaft and placed in the same frame. When this 
mighty turbo-generator, as it is called, is working at full 
capacity, pouring out a steady stream of electrical energy, 
no moving parts are visible to the casual observer, and there 
is a total absence of noise and clatter. Only a faint hum, 
bespeaking a mighty hidden force, is heard. The steel 
frame of the engine is so steady that a silver dollar can be 

66 


ELECTRICAL ENERGY 


balanced upon its edge on top of the frame while the turbine 
is whirling at full speed (Fig. i). 

The current produced by the turbo-generator is carried 
on heavy insulated cables to the switchboards and instru¬ 
ments. After being measured it is sent out over the various 
distribution lines to all parts of the circuits. 

The water-wheel-driven plant differs but little from the 
steam-plant, except no coal has to be burned as a source 
of energy. There is really very little difference between a 



Fig. 1 

HORIZONTAL CURTIS STEAM TURBO-GENERATOR 


modern high-pressure water-wheel and a turbine steam- 
engine. Both work on the same principle. In the steam- 
turbine the streams of high-pressure steam are directed 
against the revolving blades of the turbine. Impinging 
against these curved blades, the steam gradually gives up its 
energy as it passes from stage to stage through the engine 

^7 










HARPER’S EVERY-DAY ELECTRICITY 



Fig. 2 


HORIZONTAL STEAM-TURBINE SHOWING BLADES 


(Fig. 2). In the modern water-wheel the water, under pres¬ 
sure due to the fall, is directed against the curved blades of 
the turbine water-wheel and made to give up its energy, 
which is imparted to the wheel. The electric generator is 
usually direct connected on the same shaft and mounted 
either over or by the side of the water-wheel. Thus the re¬ 
volving part of the generator turns with the water-wheel. 

The current generated in the water-wheel plant is dis¬ 
tributed much the same as that produced in the steam-power 
plant. 

Loss in Producing Electricity from Steam 

There is a tremendous loss in producing electricity from 
steam. Coal is the energy of the sun, stored up for our use, 

68 















ELECTRICAL ENERGY 


In order to convert this energy into electricity it has to pass 
through various stages, and not without serious loss. 

Assuming that the energy stored in coal is ioo per cent., 
then 29.68 per cent, of this is wasted in the furnace in 
converting the energy of the coal into steam energy. Of 
this steam, representing 70.32 per cent, of the coal-energy, 
89.9 per cent, is lost in heat waste and 1.5 per cent, in 
friction. So that actually only 5.3 per cent, of the heat- 
energy of the coal is transmitted by the -engine to the 
generator. The total losses en route to the generator 
equal 94.7 per cent, of the coal-energy. 

The electric generator is very efficient. Of the energy 
supplied it by the steam-engine only about 10 per cent, is 
lost in resistance and eddy currents. The efficiency of an 
average generator is 
92.5 per cent. The en¬ 
ergy of the coal com¬ 
ing out of the genera¬ 
tor in the form of 
electricity will be, 
therefore, 5.3 per cent. 

X.925 only, or 4.9 per 
cent. of the original 
coal-energy. And, re¬ 
member, some of this 
is lost in transmission, 
and at the electric 
lamp we receive only 
4 per cent, of the po¬ 
tential energy of the 
coal. 

And the electric lamp wastes 95 per cent, of this in useless 

heat and gives hut 5 per cent, in light. 

69 


Hfl A/DL //V G> /#% 


&OLLER 2 . 7 . 0 % 

PfP/NG 2.3 ^~ 


E NG/fi/E ESA % 


ELECTRICAL EJ.% 

J^ /-/&WT % _ 

Fig. 3 
















HARPER’S EVERY-DAY ELECTRICITY 

If these figures are hard to understand the above example 
can be easily comprehended by referring to the diagram¬ 
matic drawing which shows the various losses (Fig. 3). 

The following summary shows the proportion of losses 
from the original supply of coal en route from the mines to 
the electric lamp: 


WHERE THE ENERGY OF THE COAL IS LOST 

PER CENT. 


Losses due to handling coal. 10 

Losses in boiler. 27 

Losses in piping. 2.3 

Losses in steam-engine. 55-4 

Losses in generator. .4 

Losses in transformers. .3 

Losses in transmission line. .2 

Losses in switches, etc. .4 

Losses in heating the lamp. 3.8 


Total losses. 99-8 

Used for lighting. .2 


Distributing Electricity About the City 

After the electricity is generated in the power-house it has 
to be distributed to the customers. 

In nearly every city there are four important electrical 
circuits for the distribution of electricity. Each of these 
circuits requires a separate set of wires or return circuits 
running to and from the power-house: the trolley or street¬ 
car circuit, the incandescent-lighting circuit, the arc or 
street-lighting circuit, the power circuit. 

Telephones, telegraphs, burglar-alarms, fire-alarms, etc., 
require individual wires and are in no way related to the 
light and power service. Sometimes they are customers of 

70 
















ELECTRICAL ENERGY 



Fig. 4 


the lighting company, to a certain extent, buying current for 
their storage batteries. 

Electricity is sent out from the power-house, or central 
station, over one set of wires to supply current for the light¬ 
ing of homes, offices, factories, etc. This current usually 
enters the building at a voltage, or pressure, of no volts 
(Fig.4). In case this 

lighting service ex- _ \ Am ^ Lam ps 

tends for miles 
beyond the power¬ 
house a higher volt¬ 
age is used on the 
transmission lines 
which is “stepped down” to the proper amount for the 
home by use of a small transformer located on the elec¬ 
tric-light pole in front of the house. For shorter dis¬ 
tances the current is sent out at about 220 volts, and by the 
use of a third, or neutral, wire in the house-wiring no 
voltage is available. 

But the house-lighting circuit in this day and age is also 
used for small motors, heating-devices, etc. In fact, any 
such electrical device of the proper voltage can be used on 
the house-lighting circuit, providing it does not consume 
more than 600 watts of electrical energy. If it consumes 
more than this it will surely blow the fuses , and this is a sign 
it is dangerous to use such a device , providing , of course , the 
fuses are in good condition and not weakened by long service. 
As a rule any device that will blow a six-ampere fuse is too 
heavy for household service. 

If larger motors or more extensive heating and cooking 
service is desired the electric-light company will cheerfully 
install an additional circuit in the house. And this is also 
better for the customer, as he can secure a better rate per 

7i 
















HARPER’S EVERY-DAY ELECTRICITY 

kilowatt for heating and power than for ordinary lighting. 
Like any other commodity, electricity can be purchased 
cheaper in large quantities. 


Lighting the Streets 



It requires another set of wires for the street-lighting 
service. Inasmuch as the street-lamps are not in use in 
the daytime the household-lighting wires are not used for 
this purpose, except in very small installations in villages 
where all-day electric service is not available. In the cities 
where series, high-voltage arc-lamps are used a special 
circuit for the street-lamps is always installed. With this 
arrangement the street-lamps can be switched on and 

off independent of 
all other circuits 

(Fig. s). 

Another circuit 
must be provided 
for the trolley-cars. 
The lighting circuit 
is usually alterna¬ 
ting current, but di¬ 
rect current must 
be supplied to the 
trolley-cars. All are familiar with the trolley-wire. The 
current, usually at a pressure of about 500 volts, is sent out 
over this trolley-wire, and after it passes through the trol¬ 
ley-car motors, via the trolley-wheel, the trolley-pole, etc., 
it returns to the power-house by way of the steel rails, or 
short-cuts, through the earth over a ground return (Fig. 6). 

Another circuit is provided for the power-load in cities 
where electricity is extensively used in factories and shops 

72 








finam-r 

UkSo 







i 


Fig. 5 












































ELECTRICAL ENERGY 


for power purposes. 1 his circuit is designed to carry a 
heavy current of electricity and supplies all the electric 
motors in service with electrical power. 

It is not necessary to go into the engineering details of a 
modern power-house in order to understand the distribution 
of electrical energy. It is easy enough to comprehend how 
the energy of the coal or the falling water is changed into 
electricity through the medium of the turbine and the 



Fig. 6 



generator. This energy is sent out over the city through the 
various conductors, much the same as the city water is 
distributed through various pipe systems (Fig. 7). 

In the modern city or large village we can easily draw 
water from the faucet whenever we want to. And in this 
day and age we can do the same with electricity. It is 

73 



























































HARPER’S EVERY-DAY ELECTRICITY 


always ‘ ‘on tap ” in the home or office or factory, and we 
can use just as much of it or just as little as we desire. 

Measuring the Current 

When we draw water at the kitchen sink it first passes 
through a water-meter. This measures the exact amount ot 
water we use, and we pay for it accordingly at so much a 
gallon or cubic foot. 

When we use electricity for light, heat, or power the 
current flows first through the electric meter, which measures 
the exact amount of energy we consume and pay for at so 
much a kilowatt-hour. 


\ 


Chapter VIII 

ELECTRIC CIRCUITS AND HOW THEY ARE INSTALLED 

T HERE are several different methods of installing house¬ 
hold electric circuits. These several systems may differ 
somewhat in their constructional details, but the idea of a 
return circuit must always be incorporated. It is not the 
electricity which is used, but the energy of the flowing current. 

Referring again to the comparison of electricity to water 
in a pipe, it is apparent that if current flows into the house 
ways and means must be provided for it to flow out again, 
or it will cease to flow entirely. 

If a small water-motor is placed on the kitchen faucet to 
run the washing-machine a way must be provided for the 
exit of the water which passes through the motor, or the 
wheel would not run. It is not the water which turns the 
wheel, but the energy of the water. The water-wheel 
could be immersed in a pan of water, but it would not run, 
because the water possesses no apparent energy. If the 
water is carried into the house through a half-inch pipe 
under a pressure of ioo pounds to the square inch of pipe 
it will not flow unless another pipe is arranged so as to 
carry away the used water. If these two pipes are arranged 
side by side and connected by a number of tiny water¬ 
wheels which can be turned on and off like an electric 
lamp the current will begin to flow the instant any one of 
the wheels is turned on (Fig. i). 

75 ’ 


HARPER’S EVERY-DAY ELECTRICITY 


There is no flow, no motion in the pipe A until an outlet is 
provided at the water-wheel B, although the pressure in the 
pipe A is constant. As soon as the valve is turned to the 
wheel B the flow begins, and some of the energy of the water 
is turned into mechanical energy by the wheel. The water 
flows on out of the pipe C to its original source. Of course, 
some of its pressure, or energy, is gone, having been turned 
into mechanical energy. 

In this way it is easy to understand that the pressure, or 
voltage, is constant in the electric-light wires even though 




Fig. 4 

there is no flow of current. The instant a lamp is switched 
on the current begins to move, and it is this force which 
is changed into light-energy (Fig. 2). 

The voltage, or electrical pressure, is constant at A and B, 
but the current cannot flow until the lamp switch is turned 
at C. This permits current to flow from A to B through the 

76 



































V 


ELECTRIC CIRCUITS 


lamp C and thence back to its source in the power-house. 
In passing through the lamp C some of the electrical energy 
is turned into light-energy, but the volume of the current 
remains the same. This is true because the electricity is 
not burned in the lamp. Only its energy is consumed or 
changed into light. 

The Two-Wire Circuit 

The two-wire circuit is commonly used in wiring houses 
and buildings for electric light where the current is not 
carried over any considerable distance. The two-wire 
circuit, as its name implies, consists of a single circuitous 
path through two parallel wires. The lamps, or other 
electrical devices, are merely connected in parallel between 
the two wires, thus completing the circuit (Fig. 3). 

The two-wire system is the simplest, but it is the most 
expensive, and expense is an item to be seriously considered 
in large installations. For ordinary household use and for 
small installations this item of expense is too small to be 
seriously considered. The two-wire system is so simple it 
can be easily understood by the layman, and this simplicity 
counterbalances the cost. 

The Three-Wire Circuit 

By doubling the voltage of any circuit the line loss is only 
one-quarter as great. By transmitting the current at 220 
volts wiring can be used having only one-quarter the area 
that would be necessary at no volts. In other words , a 
smaller wire could be used for the higher voltage , which would 
mean a great saving in the cost of copper. This saving, by 
nearly doubling the voltage of the line, has led to the 
establishment of the 220-volt three-wire circuit, especially 

77 


HARPER’S EVERY-DAY ELECTRICITY 


in the cities. Lamps of no volts are standard, and if they 
are to be used on 220-volt circuits they must be arranged 
two in series. Ordinarily this would compel one to burn 
two lamps at once. If three lamps were wanted four would 
have to be burned, and so on. To avoid this a third wire is 
employed, called a neutral, which composes the three-wire 
system (Fig. 4). 

The neutral wire is usually the same size as the others. 
In a three-wire system of this kind there is only three-eighths 
as much copper as in a two-wire system. This is a con¬ 
siderable saving where a whole city is wired. 

The Conducting-Wires 

Pure copper wire is generally used for house-wiring be¬ 
cause it is the best and cheapest conductor of electricity 
available. Its resistance is very low compared with 
aluminum or iron wire. A copper wire one-tenth of an inch 
in diameter has a resistance of one ohm in a thousand feet. 
An iron wire of the same size has six times the resistance. 

Never substitute an iron wire for a copper wire of the same 
size in a lighting circuit. 

In installing electrical circuits it is important to know the 
line resistance. All this data is now collected in tabulated 
form and is easily available. If we know the resistance of a 
hundred feet of a certain size wire we can find the resistance 
of a thousand feet by multiplying by ten, and so on. The 
resistance of any copper wire depends upon the length and 
diameter of the wire. 

Example. The resistance of a copper wire one-tenth of an inch in 
diameter is one ohm per 1,000 feet. What is the resistance of 6,000 feet? 

1,000 feet = i-ohm resistance 
6,000 feet = 1 X 6, or 6 ohms 

78 


ELECTRIC CIRCUITS 


In this case the resistance of 500 feet of the same wire 
would be one-half ohm. 

The resistance also depends upon the diameter of the wire 
as well as upon its length. The area of the end of the wire 
is known as the cross-section. If a square wire is used, 
measuring one inch on each side, its cross-section would be 


A 


1 in 


B 



Fig. 5 



Fig. 6 


one square inch. If the diameter of this wire was doubled, 
making it two inches on each side, its area would be four 
times as large, or four square inches (Fig. 5). 

The cross-section of A is one square inch. In B the 
dimensions are doubled, it being two inches along each side, 
but the area, or cross-section, is quadrupled. In plainer 
words, A contains enough copper to make four wires the size 
of B. Therefore, it will carry four times the current at the 
same resistance as A, or the same current at one-quarter the 
resistance. 

A wire four inches square will make 16 wires one inch 
square; a wire six inches square will make 36 wires one inch 
square. In simple arithmetic the cross-section of a square 
wire is always equal to the square of its diameter. 

If the resistance of a certain wire is one ohm to every 
hundred feet the resistance of four similar wires connected 
in parallel will be but one-fourth of an ohm, because the 

79 







HARPER’S EVERY-DAY ELECTRICITY 


current can flow through the four wires four times as easy 
as it could through the single wire. 

If the resistance of ioo feet of inch square copper wire is 
one ohm, the resistance of ioo feet of two-inch wire will be 
1^4, or .25 ohm. The resistance of 100 feet of three-inch 
wire will be 1-^9, or .0111 ohm. 

Inasmuch as wire is always drawn in circular form we 
cannot figure the area in square inches. The rules for 
figuring square wire apply also to round wire (Fig. 6). 

The cross-section of B is nine times the area of A, or 
contains the same area as nine wires one inch in diameter, 
if the parts projecting beyond the large circle are used to 
fill the chinks left inside. 

The area of a round wire is determined in circular mils. 
A mil means one thousand. An imaginary wire 1-1,000 of 
an inch in diameter has been adopted as the unit for round 
wire. It is called a circular mil. A wire 10-1,000 of an 
inch in diameter contains 10x10, or 100 circular mils. This 
method of determining the cross-section of a wire in mils is 
easiest and best because to find the area in square inches 
would involve large fractions and hard examples. 

Any circle will contain the equivalent of as many unit circles 
as the square of the diameter in mils. 

The unit wire is the mil-foot, or a copper wire one foot long 
and 1-1,000 of an inch in diameter. A mil-foot of copper 
has a resistance of 10.4 ohms. With this as a unit we can 
easily compute the resistance of any length or size of copper 
wire. 

Example. If the resistance of one foot of wire one mil in diameter is 
10.4 ohms, what would be the resistance of a wire one foot long and 10 
mils in diameter? 

A wire with a diameter of 10 mils is equivalent to 10x10, 
or 100 wires one mil in diameter, since it contains an area 

80 


ELECTRIC CIRCUITS 


of ioo circular mils. If 
the resistance of a wire 
one mil in diameter is 
10.4 ohms the resistance 
of a 10-mil wire is equal 
to 10.4-MOO, or .104 ohm. 

After we have deter¬ 
mined the resistance of a 
foot of wire we have only 
to multiply this by the 
length, and we have the 
total resistance of any 
number of feet as desired. 

In the above example 
the resistance of 1,000 feet 
of 10-mil wire would be 
.104x1,000, or 104 ohms. 

To find the resistance 
of any length of any size 
wire multiply the resist¬ 
ance of a mil-foot, 10.4 
ohms, by the length in feet, 
and divide by the circular- 
mil area. 



Battery Cell 

D. C, 
Generator 

^ A. C. 
Generator 

Motor 



Incandescent 

Lamp 

Arc Lamp 

Resistance 



Switch 


Voltmeter 



. A . 






Fig. 7 


SYMBOLS 


Ammeter 

♦ 


Resistance of wire = 


resistance per mil-foot X length in feet 
circular-mil area 


Knowing the length and the size of a wire and the current 
it is to carry, it is easy to compute the voltage drop, or loss 
of voltage due to resistance, in the wire. 

The voltage drop in a copper wire 2,000 feet long and 
.204 inch in diameter with a current of 40 amperes is 20 
volts. 


6 


81 















HARPER’S EVERY-DAY ELECTRICITY 


Volts = amperes X ohms 

mil-foot resistance X length of wire 


Resistance 


circular mils 
io. 4 X 2,000 _ 

204 X 204 
.5 ohm X 40 amperes = 20 volts 


Resistance 


= .5 ohm 


While it is best for the amateur to figure out several exam¬ 
ples of this nature so he will understand the process, this 
data is given below in tabulated form. 

Every conductor offers some resistance to the flow of 
electricity. This resistance changes some of the electrical 
energy to heat energy. Therefore every copper wire has a 
certain capacity, and any current in excess of this amount 
will heat the wire to the danger-point. Engineers have 
adopted the following tables showing the carrying-capacity 
of different size wires: 


ALLOWABLE CARRYING-CAPACITIES OF COPPER WIRES, AND 

OTHER DATA 


B. & S. 
GAGE 

DIAMETER, 

INCHES 

CIRCULAR 

MILS 

AMPERES, RUBBER 
INSULATION 

Old New 

Rating Rating 

AMPERES, OTHER 
INSULATION 

Old New 

Rating Rating 

RESIST¬ 
ANCE PER 
1,000 FT. 
AT 75 ° 
FAHR. 

WEIGHT 

PER 

1,000 FT. 
IN LBS. 

18 

.04 

1,625 

3 

3 

5 

5 

6.21 

4-5 

l6 

•05 

2,583 

6 

6 

8 

10 

3-97 

7-8 

14 

.064 

4,106 

12 

15 

16 

20 

2-53 

12-5 

12 

.08 

6,530 

17 

20 

23 

25 

1-589 

19.8 

IO 

. IOI 

10,381 

24 

25 

32 

30 

1. 

3 i -5 

8 

. 128 

16,510 

33 

35 

46 

50 

•63 

50 

6 

. 162 

26,250 

46 

50 

65 

70 

•392 

79 

5 

. 181 

33,ioo 

54 

55 

77 

80 

■3i 

100 

4 

. 204 

41,740 

65 

70 

92 

90 

. 248 

126 

3 

. 229 

52,630 

76 

80 

110 

100 

.197 

L 59 

2 

•257 

66,370 

90 

90 

131 

125 

■T 57 

200.5 

1 

.289 

83,690 

107 

100 

156 

150 

.123 

253 

0 

•324 

105,500 

127 

125 

185 

200 

.099 

3i9 

00 

•364 

133,100 

150 

150 

220 

225 

•0 77 

402 

000 

.409 

167,800 

1 77 

175 

262 

275 

.063 

506 

0000 

.460 

211,600 

210 

225 

312 

325 

•05 

640 


•633 

400,000 

330 

325 

500 

500 

.025 

1,211 


.708 

500,000 

390 

400 

590 

600 

.02 

i,5H 


•774 

600,000 

450 

450 

680 

680 

.0168 

1,817 


.836 

700,000 

500 

500 

760 

760 

.0143 

2,120 


.895 

800,000 

550 

550 

840 

840 

.0125 

2,422 


82 



























ELECTRIC CIRCUITS 


RESISTANCES PER MIL-FOOT 


MATERIAL 

OHMS PER MIL-FOOT 

Aluminum. 

i 8.7 

Copper, annealed. 

/ 

10.4 

Copper, hard-drawn. 

IO.65 

90 

64 

I14-275 

283-3OO 

600 

Iron, annealed. 

Iron, soft. 

German silver. 

Special alloys. 

Nichrome. 



The symbols used in the electrical industry should be 
learned by every amateur electrician (Fig. 7). 



# 















Chapter IX 


INDOOR WIRING SYSTEMS 

A COMPLETE metallic circuit must be installed for 
conducting the electrical energy to and from the 
points where it is to be used. 

The proper placing of such conductors is termed electric 
wiring. 

Electric wiring for buildings of all kinds must be installed 
in accordance with the rules and regulations set down by the 
National Board of Fire Underwriters. These rules are 
published in the National Electric Code. They should be 
followed closely, with such other local requirements as are 
necessary in order to secure fire protection through in¬ 
surance. These rules cover everything, from the proper 
size of wire to insulators, switches, outlets, fuses, etc., and 
the manner of installing same. 

There are four methods of interior wiring, each approved 
by the underwriters, as follows: open, or exposed, work; 
molding work; concealed knob and tube work; interior 
conduit and armored cable work. 

Open, or exposed, wiring is the cheapest and at the same 
time it is one of the safest and best methods, as the wires 
are constantly in sight (Fig. i). This style of wiring is 
generally used in barns, sheds, mills, and factories where 
the appearance of the wires on ceilings and walls is of no 
great importance. It is also extensively used in the home. 

84 


INDOOR WIRING SYSTEMS 


It is really a good way of wiring an old house, because floors 
and walls do not have to be ripped up to install this system 
of wiring. The wires can be painted the same color as the 
walls and ceilings and thus made hardly noticeable. 

The wires used for open work must be well insulated. In 
damp places, as in the basement or cellar, rubber-covered 
wire should always be used. 

For house circuits of 120 volts or less No. 14 heavily in¬ 
sulated copper wire is suitable. These wires are supported on 
porcelain insulators, made especially for this purpose, which 
separate the wires two and one-half inches from each other 
and keep them at least a half-inch from the walls. This 
half-inch of air space is one of the best insulators. It 
requires nearly 20,000 volts of electrical pressure to break 
down one inch of air space. As it would take 10,000 volts 
to leap across a half-inch of dry air, the no-volt circuit is 
entirely safe for this distance. 

The wires should always be protected with porcelain 
tubes where they pass through partitions, walls, or ceilings, 
and where they pass over pipes and other wires, iron girders, 
etc. (Fig. 2). 

The tubes should always be long enough to reach entirely 
through a partition or floor and project at least half an inch 
on each side. In making short corners and bends with open 
work the wires should receive additional support (Fig. 3). 

In making taps, or branch lines, the wires should be 
reinforced with a bit of porcelain tubing wherever they 
cross (Fig. 4). 

Molding Work 

Molding work is still used to a certain extent, although it is 
rapidly giving way before armored cable work, as the latter 
is much easier to install. In this style of wiring the wires are 

85 


HARPER’S EVERY-DAY ELECTRICITY 


run along the walls and ceiling, but they are concealed from 
view by wooden molding. This molding is made in two 
pieces. The wires are placed close together in grooves 
provided for that purpose and covered with a wooden cap, 
which is fastened in place with small screws. The size of 
the molding varies with local requirements and regulations. 
It is grooved for either two or three wires, depending on 
whether it is to be used for two or three wire circuits. The 
capping is made to conform with the woodwork in the room, 
and is, therefore, less conspicuous than open wiring. It 
cannot be used for concealed wall and floor work and should 
never be installed in damp places. Approved rubber-covered 
wires should always be used with this molding. The same 
precautions should be taken in passing through floors and 
ceilings to add the porcelain tubes as with open wiring 

(Fig- 5 )- 

Metal molding is also extensively used in wiring old houses. 
This has the advantage of being vastly smaller in size and is 
more easily concealed from view. Special fittings are made 
for this system of wiring, and the metal cover should always 
be thoroughly grounded (Fig. 6). 

Knob and Tube Work 

Concealed knob and tube work is the cheapest way of 
wiring new houses, but it is hardly to be recommended. 
The wires are all concealed within the walls and beneath 
the floors. Only approved rubber-covered wire is used. 
This wire is supported by knobs and tubes on the joints and 
studding. Otherwise it is insulated by at least an inch of 
air space. Each wire should be covered with a piece of 
insulating tubing at all outlets, switches, distribution cen¬ 
ters, etc. Where the wires pass through beams, joists, 
etc., they must be protected with porcelain tubes. They 

86 


INDOOR WIRING SYSTEMS 


p 

\ r\ 

• 




i: 


'<z> 


~<z> /\ 


.o 


+ J P- 


-C-ir 


Z'/z >r). 

Porcelain Cleai 

Fig. 1 


1 



PaHiiio*} 

Fig. 2 


^Tobe- 


^Wn 


It 


Fig. 3 


Wire^ 



IF Tubfc— 

£ 


$1 

I^Tobe-— 

Wfre^- 


5^1 


tee 


Wire>- 


Amirra-mam <<<<"<<< > « >- 




lC(i(((((((((t( ( «<<!«<< < ■ « < ' 


/S7 7S 7 77 7 7 T7 7 s rr r; 


l§=?C^-Wire- 


5ectior) of moulding 


^|g^}-Wire- 


Cross- sectiorj 

Fig. 5 



Metal Moulding 

Fig. 6 


Flc 


} 

i 

\Tubfe 



Wire’ 


Porcelain Tube 


(Veiling 


o 


o 


o 


o 


Wires^as'tened toyloor jo>St 
by y£>orcelain Knobs 


Fig. 7 



Flexible Steel Armoured CabLa. 


Fig. 4 Fig. 8 

should also be protected in this way at all contact-points 
and where they pass over beams, pipes, etc. (Fig. 7). 

Protecting the Wires with Pipe 

For new buildings the insulated wires are pulled into iron 
pipes. These pipes are built in the walls and ceilings, 

87 


























































































































HARPER’S EVERY-DAY ELECTRICITY 


completely out of sight. This is the safest and best way to 
wire a building, although costly. It can hardly be installed 
after the house is built. For old houses the flexible armored 
cable is employed. In this case the insulated wires are 
protected from injury by flexible steel armor (Fig. 8). 


Armored Cable' Wiring 



5w!tch; 






...... awwBwaa 

BASEBOARD AtnOVlD anO fiOORjg 


WlRtS FOR CHANO AND SWITCH OUTLttsN 

'FISHED"THR0U6H WITHOUT TROUBLE 
OR DAMAGE 




outlet 


V—C I 


METER and 
■ CUTOUT < 

I B0X 


Where the wires are exposed to dampness lead-covered 
cable is used. To install the cable holes are bored in 
the joists and studding, and the cable is merely pulled 

into place and fast¬ 
ened with metal 
straps. This cable does 
not require extra in¬ 
sulation. Being flex¬ 
ible and of small size, 
it can be “fished ” be¬ 
tween the ceilings and 
along the floors of old 
buildings, making it 
possible to install a 
system of concealed 
wiring without tear¬ 
ing up floors, taking 
off plaster, etc. To 
fish a wire between 
the walls a steel tape 
or a light steel chain 
is dropped down in¬ 
side the partitions. 
The end of the flexi¬ 
ble cable is attached to the fish-wire and drawn into place. 
This is the quickest and safest way to wire an old building 


Fig. 9 


88 



































































































































































INDOOR WIRING SYSTEMS 


for electric lights where it is important that the work be 
concealed (Fig. 9). 

Service Wires 

Usually the supply of electricity is brought to the house 
from some outside service, such as the distribution-wires 
of the electric-light company. Care must be taken in 
bringing these wires into 
the house. If the wires 
are overhead and taken 
in the upper rooms or 
attic they must be fast¬ 
ened to the house with 
glass or porcelain insula¬ 
tors and be provided 
with drip-loops. Where 
the wires pass through 
the siding they must 
also be further protect¬ 
ed with heavy porcelain tubes (Fig. 10). 

By slanting the porcelain tubes and arranging the drip- 
loops the rain cannot follow the wires into the house, causing 
dampness and leaks and thus destroying the insulation on 
the wires. 

The distribution-board, from which the current is con¬ 
trolled, should be located as near the center of the load as 
possible. In this way the various branch circuits will be 
nearly the same length. The distribution-board, consisting 
of a double-pole switch and fuses for each circuit, should be 
incased in a fireproof box. Such a box is usually made of 
wood and lined with asbestos paper. 

In wiring barns, sheds, and small buildings the open wiring 
may be installed, but it is best and safest to use the armored 

89 












HARPER’S EVERY-DAY ELECTRICITY 


cable, which costs but a little more and is cheapest in the 
end. 

Where the circuit passes outdoors from building to build¬ 
ing wires covered with weatherproof insulation should be 
used. They should be suspended from heavy glass or 
porcelain insulators, being tied in place with a bit of insu¬ 
lated wire (Fig. 11). 

The same care must be taken when entering a barn 
building, as noted above under the subhead of “Service 
Wires/’ A small distribution-box should be installed. 
Usually a single knife-blade switch and a set of fuses will be 



sufficient. Every circuit and every branch circuit should be 
properly fused. 


Installing the Fuse 

The fuse is the weakest place in the entire circuit. It is 
made so purposely. It is a safety-valve for the household 
wiring. The method of fusing a house circuit is best shown 
in Fig. 12. 


90 









INDOOR WIRING SYSTEMS 


lo the right of the meter the two sets of plugs protect 
their separate circuits. Here it should be said that the 
National Board of Fire Underwriters has placed a limit on 
the number of lights, fans, and other appliances that may 
be used on a circuit protected by one pair of fuse-plugs. 
And the quantity of electricity which that circuit could be 
made to carry in comparative safety is far in excess of 
what that circuit is ever permitted to receive. For example, 
if 50 amperes of electricity is known to raise above normal 
the temperature of a certain size wire the safe carrying- 
capacity of that wire, as ruled by the underwriters, is far 
below 50 amperes. And switches, lamp-sockets, and all 
other fittings are marked along the same safe lines. 


Wires by which the 
Current frttens 


II 




ft 


$ 






r 


Meter 

I 


L 



OOOOOQ 




Circuit Aio.t 

Circles Represent Lamps, Motors, 
Cooking Utensils, Carting irons and 
other Current Consuming Devices 

0 0 0 0 0 0~Q~p~ 


Circuit iVo.S 


Fig. 12 


To return to the drawing, circuits No. I and No. 2 
would be protected with nothing less than six-ampere plugs. 
The main fuse-block would be supplied with plugs of twice 
that carrying-capacity, so that, whereas the main fuse- 
plugs would take care of any short circuits or excess current 
that might occur in the main switch or in the meter, the 
other and smaller fuses would afford individual protection 
to their respective circuits. And, though the flash occa¬ 
sioned by the blowing of these fuses could hardly escape the 
fireproof casement of the plugs, still, as a matter of extra 
precaution, the fire underwriters’ rules require in most 

9i 















































HARPER’S EVERY-DAY ELECTRICITY 

cases all fuse-plugs and circuit switches to be inclosed in 
metal or other non-inflammable cabinets. If a wooden 
box is used it should be lined with asbestos paper. 

Great care should also be taken 
in installing lamp-sockets and out¬ 
lets. Only enough insulation should 
be scraped from the wire to make 
the necessary connections. The 
insulated wire should be pulled far 
enough into the porcelain base of 
the socket so as to form a com¬ 
plete protection. Never leave an 
exposed wire. If it so happens 
that a naked wire appears it should he carefully wrapped 
with insulating-tape (Fig. 13). 



Kigl)t way Wrong way 

Fig. 13 


Branch Circuits 

The load for the average branch circuit should never 
exceed 550 watts. It is far better to keep on the safe side 
of this. Ten 55-watt lamps is a big load for a No. 14 wire 
circuit. It would be better to divide this into two circuits. 
It is always better to figure out the load for the various 
circuits in accordance with examples given in Chapter VIII 
so as to be on the safe side. This is especially true where 
heating and cooking devices or small motors are to be used 
on house-wiring circuits. 

Under no circumstances must any one replace a blown 
fuse with a bridge or a fuse made to carry more than the line 
will safely hold. Time and time again it has been found 
that fires were caused by some one, totally ignorant of the 
uses and abuses of electric wiring, repairing a broken fuse with 
a bit of copper wire, thus eliminating this important safety 

92 












AC. 

DC. 

-Hll 


Symbols and Abbreviations. 

Alternating current. 

Direct current 





Cells in series. State number and type. 


Direct current bell. 



Direct current generator. 


Alternating current generator. 



Rectifies 



Direct current motor. 


Alternating current motor. 



Ammeter. 



Voltmeter. 



Wattmeter 



Ground connection. 



Lightning arrester. 


~ 4 ~ 



Telephone transmitter^ 


Telephone receiver. 





Double pole, double throw. 
D. P D T. 


Fig. 14 













HARPER’S EVERY-DAY ELECTRICITY 


device. When the excess of current came there was no fuse 
to blow and protect the line, and a fire resulted. When a 
fuse blows repair it with a new fuse and nothing else. 

If a circuit is supposed to carry not more than io amperes 
never install a fuse of any greater capacity than this. Be 
sure the line is safe , and keep it so. 

Never make any repairs to the electric wiring , or any ex¬ 
tensions to wiring already installed , without remembering and 
enforcing every rule and precaution noted in this chapter. 

In many cases the rules and regulations require that the 
electric-light wires should be soldered at all joints. This 
is a rule well worth following, whether arbitrary or not. 



OR 


Incandescent Lamps'. 


H 

PRIMARY 

jmmJ 

tuww 

Secondary 



Wires cross. 



Wire$ join. 


Transformer with one secondary. 



Fuse. 

\ 



Fheostat. 


Fig. 15 


If they are not soldered they should be firmly spliced, 
twisted with pliers, and given an ample protecting coat of 
insulating-tape. 

The soldering of electric wiring is accomplished with a 
blow-torch and a stick of specially prepared solder. It 
requires but a few seconds to coat a splice with solder. 

94 













SCREEN PORCH 


[CuPBoAeo 


understand an architect’s drawing or an engineer’s blue-print 
it is necessary to learn these various symbols (Figs. 14-15). 
In the above reproduction of a blue-print such as archi- 

95 


Fig. 16 


P/JSSr F'LOOfS PLArf 


INDOOR WIRING SYSTEMS 

Symbols, Tables, Etc., Pertaining to House Wiring 

A symbol, or mark, has been adopted by the electrical 
Fraternity to signify the location of all electrical apparatus 
in drawings, plans, and blue-prints. To be able to read and 


CHAMoER 


KITCHEN 


SINK 


ZUPdOARD 


& 

D/NING ROOM 


LIVING © /POOH 


HALL 


CD— 

PORCH 

































































































































HARPER’S EVERY-DAY ELECTRICITY 


tects prepare for a modern house the various symbols 
are used to mark the exact location of the wall and ceiling 
lamps, the various outlets and switches, as well as the 
electric cooking and heating devices which the owner 
desires to use (Fig. 16). 


/ 



Chapter X 

CONTROLLING THE ELECTRIC CURRENT 

E LECTRICI 1 Y is brought to our homes over the service 
wires. 

It is distributed to each room over the wiring system. 
Here switches must be installed for controlling the current, 
for turning it off and on. Suitable lamp-sockets, outlets, 
boxes, receptacles, etc., must be installed for the lamps, 
heating and cooking devices, and all other electrical ap¬ 
paratus to be used. 

The ordinary lamp-socket is a very simple device. It is 
made of brass and porcelain. The two lead-wires are 
brought up into the porcelain base and fastened to the 
terminal screws of the socket. The brass lining to this 
socket is threaded so the lamp-bulb can be screwed in 
place. The mere screwing in of the lamp completes the 
circuit (Fig. i). 

The threaded brass base of the lamp is one terminal. 
The brass seat is the second terminal. These correspond 
to the terminals in the socket. When the lamp is screwed 
in place the connection is made and the current is turned 
on and off by the switch-key. 

This is only one of the many varieties of sockets on the 
market. However much they may vary in design, the 
principle is the same as that described here. 

There is but one rule for adjusting wall and ceiling sockets. 
The insulation should be kept perfect. Remove only enough 
7 97 


HARPER’S EVERY-DAY ELECTRICITY 

of the insulating-material from the wires to make a good 
connection at the socket terminals. Be sure the insulated 
wires are brought well up into the base of the porcelain socket. 

For desk-lamps, heating-devices, small motors, etc., screw- 
sockets are a nuisance. It is better to install plug recepta¬ 
cles. These are usually located in the baseboard near the 






Fig. 1 


Fig. 3 


INTERIOR OF KEY-SOCKET 


PULL-SOCKET 


floor. To make the connection the forked plug at one end 
of the flexible cord is merely pushed into the receptacle. 

The great variety of plugs, receptacles, sockets, etc., is 
best illustrated by the photographs of such devices (Figs. 
2 A, 2 B, and 2 C). 

The pull-socket is another familiar type of socket. A 
short chain provided with a small ball is pulled to turn on 
and off the light (Fig. 3). 

This type of socket is very convenient for ceiling fixtures 
which are often installed too high for a short person to reach 
the keys to turn on the lights. The pull-chain can be ex¬ 
tended to any length. 


Adding to the Comfort of Electric Light 

Just wiring the house for electric lights is not all there is 
to a good job of wiring. There are many little things which 

98 









STANDARD ATTACHING-PLUGS 




L 

| 

■I pi 


r 


i 



i f . jgjFi 


d 


METAL SHELL RECEPTACLES 


DIFFERENT TYPES OF SOCKETS, SWITCHES, AND PLUG RECEPTACLES 

FOR ELECTRIC WIRING 








HARPER’S EVERY-DAY ELECTRICITY 


are practically inexpensive but which add materially to the 
comfort and convenience of the home. The following 
conveniences may perhaps be considered in the nature of 
luxuries, but none of them entails costly equipment, and they 
add that touch of ease and refinement which gives thorough 
charm to the home. 

Side-wall Switches. Locate the side-wall switches so that 
they are beside the door which is most used in entering 



KEY-SOCKET 


LOCK-COCKET 


KEY-SOCKET 




INTERIOR OF INDICATING-SWITCH PLUG AND 

RECEPTACLE 

Fig. 2 C 


SNAP-SWITCH 


DIFFERENT TYPES OF SOCKETS, SWITCHES, AND PLUG RECEPTACLES 

FOR ELECTRIC WIRING 


the room, and on the knob side of the door, so that it may be 
handy on entering and will not be covered when the door is 
swung open. 

Three-way Switches . That is the name for the side-wall 






ioo 






CONTROLLING THE ELECTRIC CURRENT 

switches that control the upper and lower hall lights from 
either position. It is an unending comfort and protection. 

The Master Switch. A further protection against burglars 
is the “master switch’’ in the master’s bedroom, which 
throws on the lights of the entire lower floor. This is a 
great convenience when it is necessary to look over the 
house in the dead of night. 

The Closet-door Switch. In most clothes-closets there are 
dark corners. A small lamp can be installed inside the 
closet and out of the way, controlled by an automatic door- 
switch, so that as the door is opened the light goes on. 

Current-taps and Lead-cords. When there are no base¬ 
board receptacles available current-taps or double-outlet 
sockets can be placed in the fixtures to connect up any 
appliances desired without sacrificing the light. 

Wall-Switches 

When electric lights were first installed some twenty-odd 
years ago the light was turned on and off by a simple key 
adjusted in the lamp-socket. This idea still prevails in 
many sockets, although the mechanism has been improved. 
Key-sockets are all right in every way, but they are far 
from being the most convenient. 

Where key-sockets are installed it is necessary to grope 
around in the dark for the lamp before the light can be 
turned on. To obviate this nuisance the wall-switch was 
brought out. 

By the aid of small switches the lights can be turned on 
before entering the room. The switch is located beside the 
door, and the lamp can be placed either on the ceiling or 
the side-wall or in any desired spot, irrespective of the 
switch which controls it. 


IOI 


HARPER’S EVERY-DAY ELECTRICITY 

The wall-switch is a very simple device designed to make 
and break the circuit. It consists of a loop of wire running 
up to the lamp circuit, wherever that may be, and it is 
operated by a small key (fig. 4). 

It will be noted that the current must flow through the 
switch before it can reach the lamp. 1 he connection at the 



SWITCH SHOWING MANNER OF INSTALLING 


Fig. 4 



INTERIOR OF SNAP-SWITCH 


lamp-socket is turned on continuously so that when the key 
is turned at the switch the connection is made and the lamp 
lights. Another half-turn of the key breaks the circuit and 
turns out the lamp. 

These wall-switches can be located where most convenient 
to the occupants of the house. Electric lights in the home 
would not be nearly so convenient without them. With 
suitable switches the entire house can be lighted from the 
front hall or any floor at a time, and the rooms can be illumi¬ 
nated before one enters them. There is no need of groping 
in the dark, of stumbling over the furniture, of striking 
matches or carrying a dangerous light. 


Placing the Switch 

Beginning with the porch light, it is generally wise to have 
the switch either in the vestibule or on the wall of the hall 




102 


CONTROLLING THE ELECTRIC CURRENT 


at the right of the front door. This permits the light to be 
turned off and on quickly if the porch light is not allowed 
to burn all the evening. 1 he hall or reception-room light 
should also be controlled by a switch on the side-wall, but 
removed from the switch belonging to the vestibule light, 
for if the two switches are together there is danger of 
using the wrong one. Another switch for the down-stairs 
hall or reception-room should be at the head of the stairs. 
It admits of entering a lighted hall on descending the 
stairs. 

Most living-rooms connect with the hall and with the 
dining-room. For this reason two switches are desirable— 
one on the wall near the door to the hall and the other on the 
wall near the door entering into the dining-room. This 
allows of instant illumination of the room on entering from 
either direction. In this room it is preferable to have central 
fixtures, with one or more side-lights to read under. Dining¬ 
room lighting is provided by a central fixture holding several 
lights. So many artistic and beautiful electric fixtures now 
come for use over the dining-room table that the light is an 
ornamental feature of the room. The switch for this room 
should be on the wall at the right of the kitchen door. 
This is convenient for the servants, and as a rule one switch 
suffices for this room (Fig. 5). 

Wall-switches are very easy to install. The same rules 
and regulations for installing indoor wiring circuit apply to 
this work. The wires should be carefully insulated just the 
same as the lamp circuits, as the same current flows over the 
switch wires. If the open system of wiring is used through¬ 
out the house the same kind should be employed for the 
wall-switches, using the same size wire, with the same in¬ 
sulation, the same porcelain blocks, tubes, etc. 

Where the wooden molding is used for the wiring this 

103 


HARPER’S EVERY-DAY ELECTRICITY 


should also be used for the switches. The same holds true 
for the knob and tube work and for the armored cable. 


Two and Three Way Switches 

A way has been devised of installing wall-switches so it is 
entirely possible to light the lamps in the upper hall from the 
lower floor and turn them off again without coming back 
down-stairs. This is called a three-way switch (Fig. 6). 



TWO-CIRCUIT ELECTROLIER 
SWITCHES 

ist Position—Circuit—I 
2nd Position—Circuit—2 
3rd Position—Circuit—1 and 2 
4th Position—Circuit—off 


Fig. 5 



THREE-CIRCUIT ELECTROLIER 
SWITCHES 

ist Position—Circuit—1 
2nd Position—Circuit—1 and 2 
3rd Position—Circuit—1, 2, and 3 
4th Position—Circuit—off 



THREE-WAY 

SWITCHES 



THREE AND FOUR 
WAY SWITCHES 


Fig. 6 


When the switch is turned at the foot of the stairs the 
lamps in the upper hall are lighted. When the switch 

104 
















































CONTROLLING THE ELECTRIC CURRENT 


located in the upper hall is turned the lamps are extinguished, 
but, note closely, it is entirely possible to turn them on again 
from either switch. 

The Master Switch 

4 

There is a way of connecting up the lights so that 
every one can 
be turned on at 
once from one 
switch. This 
is called the 
“burglar - alarm 
switch.” Upon 
hearing any un¬ 
usual noise in 
the house every 
light can be 
snapped on from 
the upper hall 
or the bedroom. 

The manner of 
installing this 
switch is best 
shown in Fig. 7. 

Insulators 

Those materials which resist the flow of electricity are 
called non-conductors, insulators, dielectrics. 

Once dry air was thought to be the only perfect insulator. 
Now we know that wireless waves are easily transmitted 
through it. There are no perfect insulators, or at least none 
have yet been found. 

There are two ways of applying insulating-material to a 

105 



Fig. 7 






















































HARPER’S EVERY-DAY ELECTRICITY 

circuit. One is to insulate the wires at all contact-points, 
depending upon the resistance of the air for the rest. Ihe 
other is to inclose the entire wire with an insulating 
covering. 

Rubber, or its compounds, are generally used for covering 
wire. This is usually reinforced with an outer covering of 
cotton or hemp braiding to prevent any deterioration of 
the rubber. 

There are a great many insulating-compounds used in 
electrical work, but they are more for the engineer and the 
manufacturer than the layman. 

Many common materials are good insulators for ordinary 
work. Among them are the following: mica, or isinglass; 
gutta-percha; shellac; ebonite, or hard rubber; paraffin; 
glass; porcelain. 

Dry paper and cloth are good insulators for low-voltage 
circuits. 

Glass has a high dielectric strength, about 12,000 volts per 
millimeter, and for continuous voltage of about 83,000 
volts per millimeter. Water readily condenses on the sur¬ 
face, and rain-water dissolves enough of the glass to slightly 
roughen the surface so that dirt, soot, smoke, etc., accumu¬ 
late. When this becomes moist the line leakage is very 
appreciable. Experiment has shown that glass in which 
potash is used in the manufacture has higher resistance 
than the glass in which soda is used. It is suitable for line 
insulators on low or medium voltage circuits. On account 
of the varying composition it is easily broken by slight 
blows or stresses. In many places it is being replaced by 
porcelain on the low-voltage telephone and telegraph cir¬ 
cuits. 

Gutta-percha is very valuable as an insulation if it can be 
protected from air and light, both of which act to oxidize it. 

106 


CONTROLLING THE ELECTRIC CURRENT 


If submerged in water or protected by lead sheath this 
oxidation is hardly perceptible. At 46° Centigrade it softens, 
is plastic at 50°, and melts at ioo°. The dielectric strength 
of untreated gutta-percha varies from 10,000 to 25,000 
volts per millimeter. 

Lava is a mineral, and is becoming a very important 
insulating-substance. It can be machined, and does not 
shrink nor expand from the effects of moisture, and 
but slightly from heat. After having been machined 
it is baked to 1,100° Centigrade, making it extremely 
hard. 

Mica, which is used very extensively, is one of the most 
valuable insulating-materials. In nature, it is of a rock 
formation, and is a silicate of aluminum and potassium or 
sodium. This is used largely in the construction of very 
delicate electrical apparatus as well as the heavier and more 
rugged construction. This may be split down as fine as 
.006 millimeter. The dielectric strength varies from 17,500 
to 28,500 volts per millimeter, depending upon the composi¬ 
tion of the specimen. 

Paraffin is used largely to impregnate insulating cloths, 
papers, etc., and in lead-covered cable work to exclude 
moisture from splices and taps. It melts at about 64° 
Centigrade and has a dielectric strength of about 8,000 
volts per millimeter. 

Porcelain is largely used for line insulators, knobs, fittings, 
switch-bases, etc.; tensile strength per square inch, 1,800 
pounds; compression strength per square inch, 15,000 
pounds; dielectric strength, 16,000 volts per millimeter. 
At very high temperatures it loses its properties, becoming a 
fair conductor. 

The various compounds of rubber are very extensively 
used for insulated wires and cables. Several different gums 

107 


HARPER’S EVERY-DAY ELECTRICITY 


are used, but the one giving most satisfactory results is 
known as para. It is vulcanized by heating to 120° Centi¬ 
grade and mixing the proper amount of sulphur. Higher 
temperatures produce hard-rubber compounds known as 
ebonite and vulcanite. 


Chapter XI 


THE USE AND MISUSE OF LIGHT 

T O understand artificial illumination it is quite necessary 
to know the details of the process of seeing. The eye 
is certainly a wonderful piece of mechanism. There are 
really six parts to the eye—the iris, the cornea, the pupil, the 
lens, the retina, and the optic nerve (Fig. i). 

The action of the eye is very similar to that of a camera. 
Light passes through the cornea, pupil, and lens of the eye 
to the retina, and is registered on the optic nerve just as 



NATURAL EYE EYE STRAINED BY 

LIGHT-GLARE 

Fig. 1 Fig. 2 


light passes through the lens of a camera and is registered 
on the sensitive plate. The retina is far more sensitive 
than the photograph plate. It is a curtain of nerve fibers 
which end in the optic nerve and go directly to the brain. 
The lens of a camera is fixed, but that of the eye automatic¬ 
ally changes its thickness to focus the light-rays on the 
retina. This action of the lens is called the “accommoda¬ 
tion ” of the eye. When the light is bad the focusing-muscles 

109 










HARPER’S EVERY-DAY ELECTRICITY 


soon tire out trying to keep objects in focus. I he muscles 
which move the eye also get tired, and the result is eye- 
strain. The ins of the eye regulates the amount of light 
admitted to the lens. It is an automatic curtain which 
opens wide when the light is dim and shuts to a pin-point 
when the light is intense. In this way it protects the delicate 
eye nerves from a dangerous flood of brilliant light (Fig. 2). 

The proper amount of artificial light depends on how 
much it helps one to see. Glaring and brilliant lamps are 
undesirable. Too much light in the wrong place is extrav¬ 
agance. The light should be steady. Flickering lights 
produce the same effect upon the eye as when we leave 
a darkened room and step out into the glare of intense sun¬ 
light. The eye always endeavors to automatically adjust 
itself to the light It cannot keep pace with a flickering 
light without tiring in a few minutes. 

Care should be taken when installing household lamps to 
avoid unshaded and brilliant points of light. Reflected 
light from polished metal or glass, bright varnishes, and 
white paper is also bad for the eyes. 

Lamps can be so placed that they are a hindrance rather 
than a help to vision. Place an unshaded lamp before a 
picture and note how much of the picture is visible. The 
pupil tries to shut out the bright light and in so doing it 
renders less bright things all but invisible. By holding the 
hand so as to cover the bright rays the entire picture in all 
its detail is visible. 

Mankind has grown accustomed to light falling from above. 
Light coming from any other direction hurts the eyes. Light 
reflected upward from snow explains why men go snow-blind 
in the arctics. Glossy white paper often produces the same 
effect upon the eyes as snow-blindness, only in a milder degree. 

When installing new lamps in the home or changing the 

IIO 


1 


THE USE AND MISUSE OF LIGHT 

old lamps see that the flame-points of light are well screened 
and shaded with opal glass or white shades. 

Light-Streams 

The best way to understand light is to compare it with 
water. A stream of light can be directed anywhere at will. 
It can be focused to a concentrated stream. It can be 
diffused in a gentle spray to cover a large area. It would be 
folly to try to sprinkle a flower-bed with a concentrated 
stream of water under high pressure. It would tear up the 
bed, destroy the flowers, and otherwise ruin it. It would 
also be folly to try to wash high windows with a lawn- 
sprinkler throwing a fine spray of water. 

This is usually true of light. Don’t use a concentrated 
stream of light where a fine diffused spray should be used. 
Shades and reflectors should be installed to diff use and direct the 
light where it is wanted and to suit various conditions (Fig. 3). 



FOCUSING- INTENSIVE EXTENSIVE 

DISTRIBUTION DISTRIBUTION DISTRIBUTION 

Fig. 3 

Measuring Light 

Light can be measured. Its intensity is expressed in 
candle-powers. A candle-power is the amount of light 
given by a standard candle. Thus, a 16-candle-power 
electric lamp gives as much light as 16 candles. A 20- 
candle-power lamp gives as much light as 20 standard 
candles. 

111 






HARPER’S EVERY-DAY ELECTRICITY 


Ail calculations of light are based on the law of inverse 
squares. The intensity of the light varies inversely as the 
square of the distance (Fig. 4). 

Thus, in Fig. 4, the surface C, being twice the distance 


D 



from A that B is, will be lighted by the same number of light- 
rays, but, as the area is four times as large, the intensity will 

/.so- only be one-fourth. Like¬ 

wise D, which is three times 
the distance and nine times 
the area of A, will have only 
one-ninth the intensity. 

The intensity of light is 
measured with a photometer . 
This merely compares the 
light with a standard light 
source located in the instru¬ 
ment, the candle-power of 
which is known. The result 
ofatestwherea2 5-wattlamp 
was tried out to find its light 
distribution is shown in the photometric curve (Fig. 5). 

112 



Fig. 5 


LIGHT DISTRIBUTION OF A 25 - WATT 
CLEAR, WITHOUT REFLECTOR 


“MAZDA.” 

























THE USE AND MISUSE OF LIGHT 


The effect of placing a concentrating-shade above this lamp 
is shown in Fig. 6. 


Light is Easily Absorbed 


Nearly all globes or reflectors absorb some light. Of coarse 
the light absorbed is light lost. The percentage of light 



THE SAME LAMP EQUIPPED WITH A CON¬ 
CENTRATING REFLECTOR GIVES THIS TYPE 
OF DISTRIBUTION 


Fig. 6 



absorbed by various reflectors is given in the following table. 


PER CENT. 

Clear-glass globes. 5 to 12 

Light sand-blasted globes. 10 “ 20 

Alabaster globes. 10 20 

Canary-colored globes. 15 20 

Light-blue globes. 15 2 5 

Heavy-blue globes. 15 “ 3 ° 

Ribbed-glass globes. IS 3 ° 

Opaline-glass globes. 15 4 ° 

Ground-glass globes. 20 30 

Medium opalescent globes. 35 4 ° 

Heavy opalescent globes. 3° 60 

Flame-glass globes. .... 30 60 

Signal-green glass globes. 80 90 

Ruby-red globes. 85 “ 90 

Cobalt-blue globes. 9 ° 95 


113 


8 
























































HARPER’S EVERY-DAY ELECTRICITY 


From this table it can be seen that if a table-lamp is 
provided with a heavy green shade only from io to 20 per 
cent, of the light-rays are able to find their way through 
the green glass. The rest is absorbed by the glass itself. 
If this globe were replaced with a globe of alabaster white 
conditions would be exactly reversed, and 80 to 90 per cent, 
of the light would be diffused about the room and only from 
10 to 20 per cent, would be absorbed by the shade. 

Where the shade of a table-lamp acts as a light-sponge and 
absorbs most of the light it is a very expensive ornament. 
In order to obtain enough light to read by large-candle- 
power lamps have to be used to allow for the light that is 
thus absorbed and wasted. With a globe which does not 
absorb the light smaller candle-power lamps may be used, 
with a consequent saving of current and lowering of the 
monthly light bill. 

The Spectrum 

\ 

To understand this absorption of light we must study the 
light itself with the aid of a prism. Ordinary sunlight is a 
mixture of red, orange, yellow, green, blue, and violet. 
When these colors are all combined they produce a white 
light (Fig. 7). 


Normal Si 


S/fe’ 


drum 


l/ltra 

violet 



Ultra 

red 


yeitrum 



Fig. 7 


Light is supposed to be a wave-motion. The length of 
these waves varies in accordance with the color of the light. 
These light-rays are longest at the red end of the spectrum 

114 
















THE USE AND MISUSE OF LIGHT 


and shortest at the blue end. When a material reflects all 
of the rays it appears white. When it absorbs all the light- 
rays it appears black. A red cloth is red only because it 
absorbs all the other colors of the spectrum and reflects 
back to our eyes the red rays. This is easily proven by 
standing under the light from a mercury-arc tube. This light 
has no red rays. A person standing in it is as pale as death. 
1 here is no color to the skin, and the lips appear blue-black 
and mottled. 

Color Values 


Because various colors and shades depend upon the 
absorption and reflection of light-rays which compose the 
spectrum they are factors to be seriously considered in 
lighting a room. Objects appear light when reflecting those 
rays which make up white light and dark when they absorb 
them. Light walls will always give more useful reflected 
illumination than dark walls. 

The following table gives the reflecting qualities of various 
colored walls. 


INCREASE OF ILLUMINATION FOR VARIOUS COLORED 

WALL-COVERINGS 


COLOR OF WALL 


REFLECTION 


White paper. 

Chrome-yellow painted 

Orange paper. 

Plain deal (clean). 

Yellow paper. 

Yellow painted (clean) 

Light-pink paper. 

Plain deal (dirty). 

Yellow painted (dirty). 
Emerald-green paper. . 
Dark-brown paper. . . . 

Vermilion paper. 

Blue-green paper. 

Cobalt-blue paper. . . . 
Deep-chocolate paper. 


115 


.70 

.62 

•50 

•45 

• 4 ° 

.40 

•36 

. 20 
. 20 
. 18 
•13 
. 12 
. 12 
. 12 
.04 























HARPER’S EVERY-DAY ELECTRICITY 


The effective illumination in a room with orange-colored 
paper would be about twice that in a room with deep- 
chocolate paper if the lamps were the same. In other words, 
the effective illumination in a room papered with a deep- 
chocolate-colored paper would be doubled by repapering the 
room with an orange - colored paper. In very few in¬ 
stances will the increase of illumination in actual practice 
be as great as that shown by this table, due to the fact that 
the bulbs of lamps become dirty, thus lowering the candle- 
power, while the walls become dirty and dingy, thus de¬ 
creasing the amount of light reflected. Moreover, in many 
cases the lamps are not replaced when their candle-power 
falls below 80 per cent, of their initial value, at which time 
they should be considered useless. 

From this data it would appear that the most efficient 
lighting-installation would be one in which clear lamps 
are used in clear glass globes or reflectors and in a room 
finished in pure-white paper. Such an installation, how¬ 
ever, would defeat its own purpose because it would seri¬ 
ously fatigue the eyes in a very short time and would 
ultimately injure them permanently. 


Placing the Lamps 

Lamps hanging at an angle throw too much light high 
up on the walls and not enough in the center of the room, 
where it is necessary (Fig. 8). 

Where the lamps hang straight down they should be 
provided with reflectors which give the most useful dis¬ 
tribution of the light (Fig. 9). 

Indirect lighting is not as efficient as direct lighting. 
It cannot be used unless the ceilings and walls are fin- 

116 


THE USE AND MISUSE OF LIGHT 


ished very light to reflect as much light as possible 

(Fig. io). 

No reflector can increase the amount of light which issues 
fro?n the lamp. Reflectors can merely guide the light to where it 


...xfWV... 





J&P'O 

V 


JL. 




Fig. 8 


Fig. 9 


THE LAMPS HANGING AT AN ANGLE FIXTURES WITH REFLECTORS PENDENT 

THROW TOO MUCH LIGHT HIGH UP GIVE THE MAXIMUM ECONOMY OF 

ON THE WALL LIGHT 



Fig. 10 

SHOWING HOW IN “ INDIRECT LIGHT¬ 
ING ” THE LIGHT IS THROWN AGAINST 
THE CEILING AND REFLECTED 


is needed. It is a mistake to think that electric lamps and 
fixtures do not need cleaning. Dirt and dust accumulate on 
both lamp-globes and reflectors. They absorb and waste much 
light. 

11 7 
































HARPER’S EVERY-DAY ELECTRICITY 


How to Figure Cost of Light 

The amount of electricity taken by an electric lamp is 
expressed in watts. Most electric lamps now manufactured 
have the number of watts which they are rated to consume 
printed on the label on the bulb. The old-fashioned car¬ 
bon-filament incandescent lamp of 16 candle-power takes 
from 50 to 60 watts. 

To determine the cost of operating an electric lamp 
divide the number of watts it consumes by 1,000, to reduce 
it to kilowatts, and multiply the number of hours the lamp 
is to be operated by the kilowatts to obtain the kilowatt- 
hours of electrical energy. The kilowatt-hours multiplied 
by the rate per kilowatt-hour which is charged gives the cost 
of operation for the stated time. 

Watts -j-1,000 = kilowatts 
Kilowatts X hours = kilowatt-hours 
Kilowatt-hours X rate =cost 

The consumption of gas-lamps is expressed in cubic feet of 
gas per hour. The number of cubic feet of gas per hour 
taken by a burner, divided by 1,000, and multiplied by 
the cost per thousand cubic feet of gas and by the hours 
of burning, gives its cost of operation for the stated 
time. 

It is really a surprise to most users of electricity to learn 
that they are buying the current in known quantities and 
that economy in its use will make it go twice as far at half 
the cost. Suppose you had to perform a certain amount of 
work and hired a man with an engine of five horse-power to 
do it. It will be assumed that the engine takes four hours 
to do the work. Now if we call the amount of work that an 

11 8 


THE USE AND MISUSE OF LIGHT 


engine of one horse-power will do in one hour a “horse¬ 
power-hour”—this is merely an arbitrary term—it is obvious 
that the engine of live horse-power will do live horse-power- 
hours of work in one hour, or 20 horse-power-hours in four 
hours. Another man with an engine of 10 horse-power 
would do the same amount of work in two hours, for he 
would do 10x2, or 20 horse-power-hours of work. Now, 
what do we pay for—for the horse-power or the horse-power- 
hours? Obviously the latter. 

In the case of electric service we use another unit similar 4 
to the horse-power in kind but not in quantity. This unit 
is called, just for want of a better name, a watt. Thus, 
on an electric toaster, for instance, there may be seen a little 
plate on which is marked “500 watts,” which means that 
the toaster takes 500 watts of electricity to heat it properly. 
(There are 746 watts in a horse-power.) But we do not 
pay for watts any more than we did for horse-power in the 
above example. It is work, or energy, that costs money. 
Thus we establish another unit similar to the horse-power- 
hour and call it a “watt-hour,” which means the quantity 
of energy developed by a watt in one hour. Thus the 
500-watt toaster would consume 500 watt-hours of elec¬ 
tricity in one hour, or 1,000 watt-hours in two hours, i> 5 °° 
in three hours, and so on. 

When we consider large quantities of electric current it 
is convenient to use a larger unit than the watt. The one 
chosen is called the “kilowatt,” which is simply 1,000 watts. 
Similarly, the kilowatt-hour is equal to 1,000 watt-hours. 
The electric-light companies charge for their electrical 
energy by the kilowatt-hour, so this unit is very important. 
As all small lamps and apparatus are rated in watts, we must 
calculate their energy consumption first in watt-hours, and 
then divide by 1,000 to bring this to kilowatt-hours, and 

119 



HARPER’S EVERY-DAY ELECTRICITY 


finally multiply the number of kilowatt-hours by the price 
in cents charged per kilowatt-hour, the answer being the 
amount of the bill. 

The number of hours a day that these lamps are in use 
varies, of course, with the season of the year and with the 
family requirements. As an average case, suppose that the 
kitchen lamp is used three hours a day for 30 days a month. 
A 16-candle-power carbon lamp takes 50 watts. In one 
hour it consumes 50 watt-hours of electrical energy. In 
three hours (that is, one day) it uses up 50x3, or 150 watt- 
hours. In 30 days, or one month, the amount consumed is 
150x30, or 4,500 watt-hours. Dividing the watt-hours by 
1,000 to obtain the number of kilowatt-hours, it is apparent 
that in one month the kitchen lamp uses \- l /2 kilowatt-hours 
of electricity, which, at the rate of 10 cents a kilowatt-hour, 
would cost 45 cents. 

If the new metal-filament lamps were used the total cost 
of lighting would be very much smaller, although the 
initial cost of the lamps would be increased. Assuming that 
the same amount of light were used—that is, the same total 
candle-power for the same number of hours—the cost for 
current would be about one-third. A 40-watt metal-filament 
lamp will give a light of 32 candle-power, and one of these 
lamps can easily be identified by the “40W” which appears 
on a little printed tag pasted on the globe near the screw- 
plug—and so for lamps of other wattages. As a rule, when 
these lamps are employed more illumination is obtained 
than when carbon lamps are used. The light is also much 
brighter and more pleasing, its intensity being softened in 
many cases by the use of frosted lamps or light-diffusing 
globes. The following table shows a worked-out example, 
using metal-filament lamps. The cost of illumination is 
obvious. 


120 



THE USE AND MISUSE OF LIGHT 


LAMPS USED 

LAMPS 

HOURS 

A DAY 

WATT- 

HOURS 

A DAY 

KILOWATT- 

HOURS 

A MONTH 

TOTAL 

COST 

PER MONTH 
AT #.IO KW. 

Kitchen. 

I 20-C-p., 25-W. 

3 

75 

2.25 

$ .22 y 

Dining-room 

I 48-c-p., 60-w. 

1 

60 

1.8 

.18 

Living-room 

2 32-C-p., 40-W. 

2 

160 

4.8 

.48 

Bath-room . . 

I 20-C-p., 25-W. 

1 

25 

•750 

• o 

Bedroom.... 

I 32-C-p., 40-W. 

1 

40 

1.2 

. 12 

Bedroom.... 

I 32-C-p., 40-W. 

1 

40 

1.2 

. 12 

Store-room.. . 

I 20-C-p., 25-W. 





Basement . . . 

3 20-C-p., 23-W. 





Corridor. 

I 20-C-p., 25-W. 

K 

12.5 

•375 

•0 3 3 A 

Stairs. 

I 20-C-p., 25-W. 

y 

12.5 

•375 

•0 yA 

Hall. 

I 20-C-p., 25-W. 

2 

50 

i -5 

• 15 

Porch. 

I 3 2-C-P., 40-W. 











Total. 

15 lamps 


475 

1425 

£1.42 y 


Calculating Illumination 

Whenever a person is figuring on installing electric light, 
for either the home, the office, or the shop, the first question 
to be considered is the amount of light which will be neces¬ 
sary for the rooms or the work in hand. 

It is not necessary to send for an illuminating engineer to 
locate and find out how many and what candle-power lamps 
are necessary to light any given room. 

But in order to go about this work intelligently it is 
necessary to know the meaning of candle-power and foot- 
candle. 

In England and America the sperm candle is the standard 
for measuring candle-power, and the light which this will 
give at any point one foot away is called a foot-candle. If a 
standard 16-candle-power incandescent lamp be suspended 
vertically the light which it will give at a point one foot away 
from the lamp and in a horizontal plane passing through the 
filament will be 16 foot-candles. Since the intensity of the 


I 2 1 






































HARPER’S EVERY-DAY ELECTRICITY 

light varies inversely as the square of the distance, at a point 
two feet away four foot-candles will be given and at a dis¬ 
tance of four feet from the lamp one foot-candle of light 
would be the intensity, thus the unit foot-candle is derived. 

The following table, showing the desired illumination for 
various uses, is practical for all ordinary purposes. 


Bookkeeping. 

Corridor, halls. 

Depots, assembly-halls, and churches. 

Drafting-rooms. 

Desk-lighting. 

Factory, general, where individual drops are used 

Factory. 

Hotel halls. 

Hotel rooms. 

Offices (waiting-rooms). 

Office (private). 

Offices (general). 

Offices (where desk-lights are used). . . . 

Reading.:. 

Residence. 

Stores (light goods). 

Stores (dry-goods).. 

Stores (clothing). 

Store windows. 

School-rooms. 


FOOT-CANDLES 

REQUIRED 


3 

to 

5 

•5 

i i 

i 

•75 

6 ( 

i*5 

5 

f C 

IO 

2 

i i 

5 

2 

i i 

3 

4 

i i 

5 

i 

i i 

i -5 

2 

6 6 

3 

1-25 

i 6 

2-5 

2 

i ( 

3 

3 

< i 

4 

i-5 

6 i 

2-5 

i 

6 i 

3 

i 

( i 

3 

2 

( i 

3-5 

4 

( < 

6 

4 

i i 

7 

5 

i 6 

20 

2 

6 i 

3 


It must be remembered that it makes a big difference 
whether the room is finished in light or dark. Where the 
finish and paper are dark you have to provide an excess of 
illumination to make up for that which is absorbed by the 
dark finishings. Light finish and light paper reflect a great 
deal of light and make it possible to illuminate a room with 
less candle-power than one finished in dark oak and dark- 
brown paper. 

It is always well to remember that a number of small 


122 






















THE USE AND MISUSE OF LIGHT 

lights give a better distribution of light than a few lamps of 
high candle-power. 

Correcting the Light in the Kitchen 

It is at once apparent that the kitchen should be the best- 
lighted room in the house. Unfortunately, this is seldom 
the case, although the most of the household work is done 
right in this room. 

Go in almost any kitchen and you will find it lighted 
either by a single lamp fastened up against the wall in the 
worst possible place or by a small electric drop-light hang¬ 
ing down from the ceiling. Arranged without thought 
or plan, these kitchen lights are generally far too small 
to be effective. They are usually so situated that the 
worker is always standing in her own light. The best 
way to light a kitchen is to install a large incandescent lamp 
in the ceiling, equipping it with a proper reflector to diffuse 
the light evenly over the entire room. For an ordinary 
kitchen a 50-candle-power metal-filament lamp should be 
used. This lamp should be provided with a pull-socket 
and a long chain so that it can easily turn on and off. By 
suspending the chain about six feet from the floor it can be 
easily reached when the light is needed or when it is to be 
turned off. 

Side-lamps cannot be made to do the work of a ceiling- 
lamp even if high-candle-power lamps and reflectors are 
used, but they can usually be made more effective by this 
means. 

Lighting the China-Closet 

An automatic switch which turns on an electric light 
when the china-closet door is opened will save many a 
pretty and valuable dish from being broken. The china- 

123 


HARPER’S EVERY-DAY ELECTRICITY 


closet is usually situated in the darkest corner of the house. 
The interior is very dark, indeed, and it is quite impossible 
to take out the dishes and to replace them without accident. 
The dishes collide with one another, chipping the edges, 
knocking off the handles, and often enough cracking or 
breaking expensive china. 

With a little ingenuity a spring can be so arranged that the 
opening of the door will automatically light a small electric 
lamp within the closet. The closing of the door turns off 
the light. The spring-switch is concealed between the edge 
of the door and the jamb or is fastened to the door-hinge. 

Lighting the Cellar 

Why will people living in houses lighted by electricity 
continue to stumble up and down dark cellar stairs when a 
small switch costing but a few cents can be installed so as to 
turn on the light in the cellarway before venturing down the 
stairs ? 

Every cellar should be equipped with electric light, and a 
small eight-candle-power lamp should be placed in the cellar¬ 
way in such a position that it will effectively light the en¬ 
tire stairway from top to bottom. This lamp can easily be 
connected with a wall-switch located in the kitchen so it 
can be snapped on before going down-stairs. An eight- 
candle-power metal-filament lamp will burn for a hundred 
hours for a total cost of but ten cents, and, as it burns but a 
few minutes each time, it can be used a year for a dime. 

1 he lamp itself costs but a few cents, and it can be installed 
very easily and quickly. 

Nearly every one has trouble to remember to turn off 
the cellar lamps. It is quite a common thing for the 
best and most thoughtful of us to forget to turn them off. 

124 


THE USE AND MISUSE OF LIGHT 


Often they burn for days without being noticed. This can 
be easily remedied by installing a buzzer on the circuit. A 
“pilot lamp,” usually of red, placed near the switch will 
help. But this, too, is easily overlooked and forgotten. A 
buzzer is by all means better. It continues to buzz as long 
as the cellar lamps are lighted and only ceases its clamor 
when you turn out the lights. There is no danger that 
even the most absent-minded will forget the little wall- 
buzzer. They cost but a few cents and are easily attached 
to the electric wires. 

Electricity for the Bedroom 

Very little care and attention is given to the placing of 
electricity in the bedroom. Apparently the contractor just 
sticks a wall-fixture in wherever it is most convenient, and the 
occupant of the room has to make the best of a bad job. 
Just as often as not the electric light is located up against 
the wall where it ought not to be. 

Not only is it important that the electric light for the bed¬ 
room be located where it is most convenient and where the 
entire efficiency of the lamp is available, but other outlets 
should be provided in case an extra lamp is desirable during 
sickness or for reading purposes. Now and then auxiliary 
electric devices, such as the small electric flatiron, the 
electric fan, the electric shaving-mug, the electric luminous 
radiator, are desired, and where only one outlet is provided 
the lamp has to be taken out whenever anything else is 
used. Of course, this is a great inconvenience during the 
hours of darkness. 

An electric shaving-mug is very serviceable in homes where 
hot water is not always on tap, and in connection with the 
shaving-mirror it is quite handy to have an electric light 

125 


HARPER’S EVERY-DAY ELECTRICITY 


that may be adjusted to render its best service. The elec¬ 
tric curling-iron and the electric hair-drier appeal very 
strongly to the ladies of the house, the former having dis¬ 
tinct advantages over the curling-iron which has to be heated 
by gas, with the accompanying soot and danger of exces¬ 
sively high temperatures. The electric vibrator is another 
apparatus which may be used in the bedroom. Fans, 
radiators, and other common devices may also be wanted in 
this part of the house. A reading-lamp which can be placed 
in a convenient position at the bedside is also a comfort 
and convenience. A number of outlets are just as desirable 
in the bedroom as in any other portion of a residence. If 
the greatest use is to be made of electric current the owner 
should bear all these points in mind when laying out the 
wiring scheme. 

Illuminating the Rest of the New Home 

Home-builders are very apt to leave the question of 
artificial illumination entirely to the architect in charge. 
This in itself is well enough, but to-day illuminating engineer¬ 
ing is an established profession, and it is very easy to secure 
reliable information on this important subject of proper 
illumination. 

The architect is too prone to lean toward the artistic in 
lamp-fixtures and placement. Artistic effect is all right 
enough, but it should always be secondary to good, healthful 
illumination. The eyes should be considered first and the 
decorative scheme last. 

With electricity it is possible always to have the lamps just 
where you want them. After the house is occupied it is 
frequently found that the lamps need changing or that 
additional lamps are necessary. If a few such minor changes 
are necessary for the comfort of the eyes they should not be 

126 


THE USE AND MISUSE OF LIGHT 


neglected. The work will really cost but little. Another 
important item which most folk overlook is the fact that 
electric lamps can be had in a great variety of sizes, from 
the little fellow of but eight candle-power all the way up 
to units of two hundred or even 500 candle-power. It 
is lolly to burn a 20 candle-power lamp where an eight- 
candle-power will answer all purposes. And it is equally 
wrong to try to read by an eight or ten candle-power lamp 
where a thirty is required. In the end the eyes will suffer. 
It is always cheaper and easier to buy suitable lamps than it 
is to purchase glasses. 

When building a new home or when planning a new 
system of illumination for the old home the following 
important rules should be most carefully considered. 

1. Always use a shade or reflector with a lamp. A bare lamp, which 
produces a glare, especially when near the level of the eye, should never 
be employed without a protecting device. 

2. When possible mount the lamps high so as to be out of the ordinary 
line of the eye. 

3. If the ceiling of your room is low use two or three small lamps 
rather than one large lamp. If the ceiling is high larger lamps may be 
used. Metal-filament lamps are made in a large variety of sizes, suiting 
them to practically all conditions in the home. 

4. Reflectors are designed for given sizes of lamps. If you use a 40- 
watt lamp secure a 40-watt reflector. Always use the reflector-holder 
which is designed for the particular lamp in question. 

5. Do not forget that too much light may be as harmful as too little. 
If your eyes become tired and hurt toward the end of the evening they 
may be either blinded by too much light or strained by an insufficiency of 
light. 

6. Keep the lamps and reflectors clean. Much larger losses of light 
due to dust and dirt occur than you would imagine. 


Chapter XII 


THE INCANDESCENT LAMP AND ITS ADAPTATIONS 

T HERE are several kinds of electric lamps. Ihe 
incandescent lamp used for ordinary indoor - lighting 
purposes is most common. 

Incandescent means literally to glow with heat. In fact, 
such a lamp is made luminous by heat. 

To the ordinary user of electricity for home lighting the 
electric lamp is but a lamp. They do not know how it is 
constructed or why one lamp is better than another. The 
life of an electric lamp, its economy and durability, depend 
almost entirely upon the little hair-like filament, or wire, 
located within the glass bulb, which glows with light when 
the electricity is turned on. No matter how nicely the 
globe and base are made, no matter what care is taken in the 
assembly of the various parts, the life of the lamp and its 
usefulness depend upon the filament. 

The incandescent-lamp filament is confined in a small 
glass globe from which the air has been exhausted to keep the 
wire from burning up. This glass globe also acts as a very 
effective shield for the lamp, making it possible to use the 
lamps very near inflammable materials without danger. 
This is especially valuable in homes where there are children, 
for they cannot possibly set fire to the house or burn them¬ 
selves with electric lamps. The electric lamp produces so 
little heat that nothing can catch fire from being blown 
against the globe. 


128 


THE INCANDESCENT LAMP 


Tip 

i 

k 





Leading-in 

Wires 

Glass Stem 


Brass Screw 
Shell of Base 


Glass Bulb-*- 

-'A' - ' * 

Cane Glass 

Hub - 


Tungsten 

Drawn-wire 

Filament 


Bottom 

Anchors 


Platinum 


Air-tight 

Seal 


Glass Insulation 


Brass Cap Contact 


Anchors 


INCANDESCENT LAMP 


If an old-fashioned carbon filament is used the light will 
be of a poor yellowish quality and the cost for current will 
be high. This is because the filament is made of carbonized 
cellulose, which is a vegetable paste. Carbon lamps are now 
out of date, being replaced by the metal-filament tungsten 
9 129 































HARPER’S EVERY-DAY ELECTRICITY 


lamps which give a better light for less cost. The tungsten 
metal is drawn into fine wire, from which the filaments are 
made. This wire is really very strong for its size, being of 
less diameter than a hair, but it has the tensile strength 
of piano-steel. 

Strange as it may seem, there are thousands of people 
who do not know that incandescent lamps can be obtained 
in almost any candle-power desired. They accept what¬ 
ever is given them and pay whatever is asked without a 
question. More than half the time a complaint for excessive 
cost of electric-lighting is traceable direct to lamps of too 
high candle-power for the light required. That cost mounts 
up in direct ratio with the increase of candle-power is shown 
by the fact that an eight-candle-power tungsten lamp will 
burn for ioo hours for a total cost of but io cents, where 
the rate is io cents a kilowatt. A 20-candle-power lamp 
on the same circuit would only burn 40 hours for 10 cents, 
and a 32-candle-power lamp but 25 hours. 

With proper glass shades and reflectors to direct the light 
where it is most needed lamps of small candle-power can be 
used with better light effect than those of high candle-power 
where the light is misdirected, absorbed, and wasted. 

Light Caused by Resistance 

The light emitted by an incandescent lamp is caused by 
resistance. The metal filament inside the glass globe re¬ 
sists the flow of current to a considerable degree. In forcing 
its way over this obstacle in its path the electricity heats 
the filament white-hot. As soon as any object is heated to 
incandescence, by whatever source, it emits light-rays. 

When you turn on the electric light the current flows over 
one conducting-wire to the lamp, then inside the glass globe, 

130 


THE INCANDESCENT LAMP 


through the tiny lead wires concealed within the glass stem. 
Here it encounters the resisting filament. But the current 
is so strong, so full of power, that it forces its way through 
the filament wire in spite of this resistance and back over the 
return wire of the circuit. Of course, it requires energy to 
force its way over this obstruction in its path. This energy 
is changed into heat-energy and from heat to light energy. 
It is this energy we pay for when the monthly light bill 
comes in. 

Experimenting with the Incandescent Lamp 

The air is exhausted from every incandescent-lamp globe. 
If air were allowed in contact with the delicate filament the 
tiny wire would be burned up in a flash. You can easily 
prove this. Take an old incandescent lamp and place it in 
the lamp-socket. It will burn steadily, evidencing that the 
vacuum is still good. Now take a pair of pliers and 
carefully break off the tip of the glass globe. This tip marks 
the place where the bulb was sealed after the air was ex¬ 
hausted. Break a tiny hole in this tip and let in the air. 
Now screw the lamp into the socket and turn on the current. 
In a flash the filament will be fused and destroyed. The 
oxygen of the air has burned it up. Without air there can 
be no combustion, hence the need of the vacuum. 

And so, to experiment with incandescent lamps we must 
have a suitable vacuum. A good vacuum is impossible 
without an air-pump. But for minor experiments a partial 
vacuum will do. 

It is possible to carry on quite an extensive experiment 
in this line by inverting a common glass in a shallow dish 
filled with water (Fig. i). 

By using rubber-insulated wires to carry the current 
through the water to the filament beneath the glass the fila- 

I 3 I 


HARPER’S EVERY-DAY ELECTRICITY 


ment may be lighted. The oxygen within the inverted 
glass will soon burn up, so it cannot destroy the filament. 

But this apparatus is very unsatisfactory. A better 
vacuum is more suitable to the task in hand. 

Secure an ordinary glass jelly-jar with a good smooth top. 
Next prepare a piece of dry hard wood four inches square 


Yilamcrj t 



Xlermio&l 

flk_, 

/ 

1 

4 

/ tSV-BW 

_ B _/ 

a m 

.I...1LL1.11 U1.3H-L/ 



B«\5e 


RW 


BW 



v v _it i«-Terminal 

Wnstjers 

Detail o/'A ( ^4arotu6 


Fig. 2 



Fig. 3 


and one inch thick by varnishing it on one side and along 
the edges, leaving one side unvarnished. Heavy shellac 
varnish should be used. This will fill the pores of the wood 
and make it reasonably air-tight. Drill two small holes 
through this wooden base an inch and a half apart (unless the 
mouth of the glass jar is smaller). These are for the wire 
terminals. As these terminals must be air-tight, small bolts 
with nuts and rubber washers must be used (Fig. 2). 

A is the wooden base, B, B are the bolts, RW is the 
rubber washer, and BW, BW are the brass washers. 
BS are the brass strips for the terminal connections. The 

l p 































THE INCANDESCENT LAMP 

terminals are split, or doubled, to hold the filament in 
place. 

With this for the base of our experimental lamp and the 
jelly-jar for the globe we are ready for the experiments. 
But first a way must be found to exhaust the oxygen from 
the globe, else the experiment will certainly fail. It is this 
oxygen of the air which fuses the hair-like filament. If the 
oxygen can be destroyed the result will be the same as 
though the air was pumped out. 

To destroy the oxygen within our globe we will burn it 
up. Wet a can-rubber, such as are used to seal fruit-cans, 
and place it on the baseboards so the glass jar can be in¬ 
verted over the terminals. Place a few drops of alcohol 
inside the rubber ring and set it afire. Now quickly invert 
the jelly-jar over the rubber, pressing it firmly in place. In 
a second or two the alcohol blaze will die out for want of 
oxygen. Without oxygen fire cannot burn. When the 
available supply is consumed the fire goes out. The pres¬ 
sure of the outside air will hold the glass jar firmly to the 
base. 

A vacuum made in this way will last for a considerable 
time if the baseboard is well varnished, the terminals made 
air-tight, and the rubber new and springy. It will last 
long enough for our experiments. 

This apparatus can be connected directly to the lighting- 
circuit, providing an indicating-switch is used. An indicat¬ 
ing-switch, as its name suggests, tells when the current is 
on and off. One can be purchased for a few cents. When 
the current is turned on the word “on” appears in white 
letters on a black background to indicate that the current 
is flowing. When turned off, the word “off” appears. It 
would be dangerous to use the lighting-current without this 
switch because sooner or later the operator would forget 

133 


HARPER’S EVERY-DAY ELECTRICITY 


whether or not the current was on and would try to adjust 
one of the terminals and thus get a shock. Current from 
the lighting-circuit is not dangerous, but it is best handled 
with extreme care. 

With an indicating-switch adjusted to the baseboard of 
our apparatus tiny metal wires, bits of carbon, etc., can be 
heated to incandescence in the glass jar. Of course this is 
only elementary and merely provides a way to study the 
action of the incandescent lamp. Clamp bits of fine wire 
an inch or two long between the terminals and turn on the 
current after the oxygen in the air is destroyed by the burn¬ 
ing alcohol. Experiment with various kinds of wire—brass, 
copper, iron, German silver, and even with bits of platinum 
and tungsten wire if you can get any, from old lamps or 
otherwise. Also try the pieces of filament from old carbon 
incandescent lamps or bits of carbon made from charred 
paper, thread, etc. (Fig. 3). 

A few experiments with this apparatus, crude as it is, will 
give any one a thorough working knowledge of the incan¬ 
descent lamp. 

But, after all, incandescent lamps can be purchased vastly 
cheaper than any amateur can make them. It was the 
general custom among electric-lighting stations to give away 
old carbon incandescent lamps. The new metal-filament 
lamps are a bit more expensive. 

Adaptations of the Incandescent Lamp 

# 

There are hundreds of interesting adaptations of the 
electric lamp for use about the home. In the very begin¬ 
ning it should be repeated that incandescent lamps can be 
purchased in all sizes, from eight candle-power to several 
hundred candle-power, which can be used in ordinary house- 

134 


THE INCANDESCENT LAMP 


hold sockets. Miniature lamps are also made to fit small 
candelabrum sockets, or socket-adapters, which are more in 
accord with the size of the lamp. 

As miniature lamps are all of low voltage , they should he 
always connected in series for service on ordinary household 
circuits. For instance , n lamps of io volts each should he 
used in series for a no-volt circuit. 


Illuminated House Number 


In the city it is quite important that the house number 
be illuminated at night. It is entirely possible to so arrange 
the porch light that it illuminates the house number at the 
same time. This can be done in a number of ways. Per¬ 
haps the easiest is to paint, in black letters, the house number 
on the white lamp-shade itself. Still another way is to build 
a little wooden box, with a glass front, and place the number 
on the glass (Fig. 4). 

The box houses the small porch lamp, which is controlled 



Fig. 4 




T. lb 


L a.m/6 


5 wit cl 


71 

a; 




t 


Fig. 5 

Circuit 


’jLnrtyb 


tye. 




by a switch located in the front hall. The numbers are cut 
out of black paper and pasted to the glass. 

*35 









































HARPER’S EVERY-DAY ELECTRICITY 


A good way to accomplish the same purpose is to inclose 
the porch light in a hanging-lantern, with the number 
lettered on the glass door of the lantern (Fig. 5). 

Such a lantern can be easily made of wood, with the 
dimensions about six by ten inches. The design of the 
lantern can be left to the originality of the builder, but the 
old-fashioned Gothic effect shown above is best. This 
porch lantern should be suspended from the ceiling, and 
placed low enough so the number is easily visible from the 
sidewalk. 

Drop-Light for the Work-Bench 

A drop-light is essential for the work-bench where night 
work is necessary. A fixed light is not at all suitable 
for all kinds of work. It will be in the way for some tasks, 
and not near enough for others. The light for the work¬ 
bench should be provided with a suitable green reflector, 
which will throw a strong light in a downward direction. 
The light should be made so it can be moved to any part of 
the bench and arranged so it can be easily and quickly 
raised or lowered as the work requires. 

Stretch a piece of picture-wire between two screw-eyes so 
it extends the entire length of the work - bench a little 
distance from the ceiling. Arrange a long flexible cord for 
the bench light. This double cord, covered with silk or 
cotton insulation, is made purposely for portable lights and 
costs but a few cents a foot. The lamp can be adjusted the 
length of the work-bench by placing a sliding-ring on the 
wire and fastening the cord to the ring (Fig. 6). 

The easiest and simplest way to fix the lamp-cord so it 
can be adjusted to any desired height above the bench is to 
bore two holes through a small block of hard wood and run 
the lamp-cord through these holes (Fig. 7). 

136 


THE INCANDESCENT LAMP 

A great many other ingenious ways can be devised to hold 
the lamp at any desired height. 

I here is still another combination of the drop-light- 
picture-wire system for lighting the work-bench. In this 



case the picture-wire is not fastened to the screw-eyes, but 
passed through them and affixed to counter-weights (Fig. 8). 

Suitable Lamp-Shades 

A good shade for a hanging-lamp can be made of heavy 
paper. From the local printing-office get two sheets of 
heavy paper about 30 inches by 40 inches, one sheet white 
and one of a suitable color to harmonize with the hangings 
of the room in which the shade is used. A circle 30 inches 
in diameter should be circumscribed on both sheets. These 
circles should then be cut out. Out of each a sector about 
eight inches wide should be cut away. The two pieces 

137 

























HARPER’S EVERY-DAY ELECTRICITY 


should then be placed one on top of the other with the white 
underneath, and the edges should be folded as in Fig. 9. 

When the base is about 20 inches in diameter the two 
thicknesses of paper may be fastened by round-headed brass 
paper-fasteners. These cost but ten cents a box of one 
hundred. A small hole is now cut in the top, through which 
the cord is drawn. The lamp-sockets support the paper 
shade. Be sure the paper shade does not touch the lamp- 
globe. 

Lamps for the Shaving-Mirror 

A novel and effective way to light a mirror is to adjust 
miniature lamps along the edge of the mirror (Fig. 10). 




Fig. 9 

Take an ordinary mirror and mount on it a number of 
porcelain receptacles in which are to be inserted miniature 

138 


















THE INCANDESCENT LAMP 

incandescent lamps such as are used for Christmas-tree or 
automobile lighting. These lamps can be bought at elec¬ 
trical-supply stores and are made for various voltages. 

1 he lamps should be wired in series. The wire from one 
side of the supply circuit goes to the first lamp terminal, 
from the second terminal of that lamp to the first terminal 
of the next, and so on around, connecting finally to the other 
side of the supply circuit. The number of lamps required will 
be the number of volts in the main circuit divided by the 
rated voltage of one lamp. Suppose, for instance, the 
circuit voltage is no to 112 volts (the usual house-lighting 
circuit) and your lamps are marked seven volts; the number 
required would be sixteen. If you use more lamps they will 
not glow, or if you use less they will burn too brightly and 
perhaps burn out. 

Lighting the Pantry Shelves 

The sliding-wire system mentioned for the work-bench 
can be very easily adapted for lighting the pantry shelves. 
Needless to say this system can be used with a small battery 
system of lighting and miniature low-voltage lamps, or with 
the ordinary pantry light securing electricity from the 
house wire (Fig. n). 

You will note by the diagram that the lamp-cord is pro¬ 
vided with a small coil-spring or a heavy rubber band, 
taped to the cord, so the lamp can be raised or lowered for 
any of the shelves. The cord can be adjusted by means of 
the small wooden block mentioned in connection with the 
work-bench lamp. 

The “ Trouble ” Lamp 

Every automobile should be provided with a ‘Trouble” 
lamp, and this little device is also very useful about the home 

139 


HARPER’S EVERY-DAY ELECTRICITY 


or the barns. The trouble lamp is so called, because it is 
generally used in looking for trouble, breakdowns, accidents, 
etc. Its field of usefulness is not confined to lighting odd 
corners, nooks, and crannies, as it is really of great service 
in any home and for a hundred uses. 

The trouble lamp consists of a long, flexible, well-insulated 
lamp-cord fitted at one end with a screw-socket for attaching 



Fig. 11 Fig. 12 


to the ordinary lamp-socket and at the other end with a lamp 
and guard. In the case of the automobile the plug should fit 
the ordinary automobile lamp-socket, and a miniature lamp, 
of the same voltage as the lamps on the car, should be used. 

The cord contains, beneath the heavy insulation, two in¬ 
sulated cables which are made of many fine strands of wire. 
Being made of many small wires, it can be bent and turned 
without kinking and breaking and will last for a long time. 
At least fifteen feet of this wire should be used. The lamp 
should be guarded against breakage. This is done by sur¬ 
rounding it with a guard of stifF iron wire arranged like a 
coarse basket. Protected in this way the lamp can be 
thrust into odd corners, dangled into the midst of wheels 
and cams, ironwork, and other places without danger of 
breaking, or it can be laid on the floor for a long time, 
while you are working, without scorching the woodwork 
(Fig. 12). 

140 










































THE INCANDESCENT LAMP 


A Dual-Purpose Lamp 

Lamps are now made with double filaments, giving two de¬ 
grees of light, which are a great convenience. By merely 
pulling the lamp-cord a two-candle-power light is available, 
pulling it again wdl give 16 candle-power. This lamp is 
very convenient for the bath-room or the hall, as the low- 
candle-power light can be kept burning all night without 
serious cost, and the mere pulling of the cord will throw on 
the high light. It saves all danger of stumbling or falling 
when one is walking about the house in a sleepy condition, 
as often happens. 


Desk-Lamps 

Every desk should have an adjustable lamp. A great 
variety of these lamps are offered for sale at very reasonable 
prices. But a good one can be easily built on the boy’s work¬ 
bench. The lamp should be of the Mission type, made of 
hard wood—mahogany, black cherry, or sumac—if it is to be 
finished with the natural grain and color, and of cherry or 
oak if it is to be stained. The lamp consists of four parts— 
the base, the pedestal, the arm, the shade (Fig. 13). 

The base is six inches square, an inch and a half thick, 
with beveled corners and edges. It is mortised for the 
square pedestal, which is firmly glued in place. The pedestal 
is ten inches high, two inches square, and slotted for the 
arm. The arm is eight inches long, two inches square, 
tongued for the slot in the tip of the pedestal, and fitted foi 
the lamp-socket and shade at the other end. There are two 
ways of adjusting the lamp-cord. Silk cord may be used, 
which is merely fastened to base, pedestal, and arm by 
ornamental brass ring-screws. Or a small hole can be 

141 


HARPER’S EVERY-DAY ELECTRICITY 


bored through the entire length of the pedestal and arm to 
admit the cord. 

The arm is fixed in the pedestal slot with a thumb-screw. 
It is raised or lowered by adjusting this screw. 1 here are no 
hard and fast rules about building this desk-lamp. The 
woodwork may be as fancy as desired, with scrollwork, 
carving, and high polish. This is a mere detail to be left 
to the discretion and energy of the builder. This lamp is 
not efficient without a suitable shade. A shade of brass is 
best. Metal shades can be purchased cheaper than they 
can be made, costing but a few cents each. But a suitable 
shade can be easily made of a sheet of tin, brass, or hammered 
copper. The latter is very ornamental. The sheet metal 
should be cut roughly, as shown in Fig. 14. 

The pattern should be about eight inches long and seven 
inches wide at the widest part. These figures are not 
definite. They should not be followed except in a general 
way. It is best to make a paper pattern, and be sure it fits 
before cutting the metal. When cut, the metal is bent and 
fastened, as shown in Fig. 15. 

After the desk-lamp is done it is easy to make a table- 
lamp of practically the same design. The Mission table-lamp 
is made of the same material and the same general construc¬ 
tion as the desk-lamp. The only material difference is in 
the shade. For the table-lamp the shade can be made of 
wood (Fig. 16). 

Lighting the Piano 

An adaptation of the above lamp is very easily made for 
lighting the piano. The details are essentially the same as 
given above. The lamp consists of a base, a short pedestal, 
and an arm, with a large fixed shade (Fig. 17). 

The base is six inches by six inches and an inch and a 

142 


THE INCANDESCENT LAMP 

** 

half thick. It is mortised for the short pedestal, which, in 
turn, is mortised for the arm. The lamp-socket is adjusted 
to the side of the arm, or two sockets are provided for two 
small lamps. The shade is made of a sheet of brass and 
two wooden end-pieces. The details are best shown in the 
diagram. 

Decorative Use of Miniature Lamps 

There is no limit to the decorative effects made possible 
by the use of miniature lamps in the home. These lamps 


Fig. 15 



come in a great variety of shapes and colors, in all small 
candle-powers. Some of them are shaped like apples, 
plums, various other fruits, flowers, manikins, animals, 
fowls, etc., etc. For balls and parties, holidays and special 
occasions these lamps can be used with wonderful effect for 
decorative lighting. 


143 


































HARPER’S EVERY-DAY ELECTRICITY 


These miniature lamps come in all voltages. When used 
on the household-service wires, from an ordinary lamp- 
socket, several of them must be used in series. Thus, ten 
12-volt lamps should be connected in series for use on a 
120-volt circuit. It would ruin a low-voltage lamp in a 
second or two to attach it directly to the ordinary high- 
voltage circuit. If too many lamps are used in series they 
will not burn bright. 

These tiny decorative lamps have been used extensively 
for table-decorating. A centerpiece of flowers or fruit may 
be very effectively lighted with these small lamps, using 
such bulbs as are shaped to resemble the fruit or the flowers. 

Miniature lamps lend themselves readily to the decoration 
of rooms. They may be festooned from the ceiling, with 
flowers or evergreens, they may be arched over doorways or 
windows, and used in a dozen other ways which add greatly 
to the decorative effect. 


Chapter XIII 

RESISTANCE, AND HOW IT CHANGES ELECTRICITY TO HEAT 

ALL known conductors offer some opposition to the flow 
A of the electric current. This opposition is well named 
resistance. In some manner, akin to friction, it retards, 
or impedes, the flow of electricity. 

To understand electric heat you must be perfectly familiar 
with this strange quality of resistance, which cannot be 
seen and is, therefore, hard to comprehend. Electrical re¬ 
sistance is very similar to friction which opposes and re¬ 
tards the flow of water in a pipe. 

Friction is opposition to mechanical motion. 

Resistance is opposition to electrical motion. 

For the sake of convenience we speak of this “electrical 
friction” as resistance. 

There seems to be no perfect conductor for the electric 
current. Even the best copper wire resists the flow of 
electricity to a certain extent. It is a significant fact that 
this resistance changes in degree when the wire is heated. 
This would indicate that the resistance is caused by some 
peculiarity of the molecules composing the metal. 

Electricity flows along a conductor in the form of a 
current , very similar to the flow of a current of water, only 
much faster. A velocity of 300 feet a second is high for a 
stream of water. Electricity flows at the rate of 186,000 

miles a second. 

10 


145 


HARPER’S EVERY-DAY ELECTRICITY 


To fully understand resistance you must remember that 
the flow of the electric current depends upon three things— 
its pressure, or potential ; the quantity of its flow, or am¬ 
perage; and the amount of resistance in its path. 

Let us see if we can comprehend this better by comparing 
it with the flow of water in a pipe. 

Now, water in a pad is measured by gallons. But water 
in a pipe is always measured by gallons per second. 1 he time 
element is always considered. We do not say there are 
ioo gallons of water in a pipe. We say the water flows 
through the pipe at a rate of 15 gallons a second. 

In this same way we never try to tell how much elec¬ 
tricity there is on a wire. We always say that so much 
current is flowing over the wire each second. The quantity 
of water is measured in gallons. The quantity of electricity 
is measured in coulombs. But “coulombs per second” is a 
clumsy phrase, and it has been happily shortened to amperes , 
which literally means coulombs per second. 

Thus the amount of current flowing over a wire is expressed 
in amperes. For example, it requires a continuous flow of 
% ampere through the filament of a tungsten incandescent 
lamp to keep it glowing on a no-volt line. The pressure 
of the current, which causes it to flow, being expressed in 
volts, and the resistance, which opposes this flow, in ohms y 
the number of amperes flowing can always be found by 
dividing the volts by the ohms. 

Volts -r- ohms = amperes 

It requires pressure to force water through a pipe. In 
hydraulics this pressure is expressed in pounds per square 
inch. It also requires pressure to force electricity along a 
wire. This electrical pressure is always expressed in volts. 
Thus your village water-supply may operate at a pressure 

146 


RESISTANCE 


of 80 pounds per square inch and your lighting circuit at a 
pressure of iio volts. \ou can find the voltage of any 
circuit by multiplying the ohms by the amperes. 

Ohms X amperes = volts 

The amount of work a certain number of amperes will do 
at a certain voltage is expressed in watts. In other words, 
the product of volts and amperes is known as watts. The 
watt is the unit of electric power. The electromotive force, 
or pressure, of one volt forcing one ampere over one ohm 
resistance will do one watt of work. The term kilowatt 
means 1,000 watts, and is practically i-J horse-power, or, 
to be exact, 746 watts equals one horse-power. The power 
transmitted by a circuit and the rating of power apparatus 
are usually expressed in watts. 

Volts X amperes = watts 

The value of the unit horse-power is understood to mean 
33,000 foot-pounds per minute. That is, a power capable 
of raising 33,000 pounds one foot in one minute against the 
force of gravitation. This unit was originally established 
by James Watt, the inventor of the steam-engine, to give 
a rating to his engine. It was found by him to be about 
equivalent to the power of a strong London draught-horse. 

If the current was measured in a lighting circuit of no 
volts, supplying eight lamps of 40 watts each, it should be 
found to be approximately 2.9 amperes. Each of the lamps 
consumes 40 watts, then the total power is 8 x 40, or 320 
watts. These are on the no-volt circuit, and, as stated 
above, watts equals volts times amperes, then the number 
of amperes would be 320 -f- no, or 2.9. 

The pressure of ordinary house-lighting circuits is about 
no volts. Voltages of no or less are considered safe. 

i47 


\ 


HARPER’S EVERY-DAY ELECTRICITY 

The trolley circuit is usually about 500 volts, and is dan¬ 
gerous. There are several other terms used in place of 
volts. It is often spoken of as potential , electromotive force , 
E. M. F ., potential difference , tension , etc . 

The ohm was named in honor of Dr. George S. Ohm, a 
famous German physicist who formulated the laws of 
electrical resistance. It has been determined that one ohm 
is the resistance of a uniform column of mercury 106.3 
centimeters long, weighing 14.4521 grams at the melting- 
point of ice. It requires a pressure of one volt to force one 
ampere of current through one ohm of resistance. If one 
volt can force but one-tenth of an ampere over a wire we 
know that the resistance of the wire is 10 ohms. Turn this 
about and you will see that this will require 10 volts to force 
one ampere through 10 ohms resistance. 

Volts -i- amperes = ohms 

Perhaps these units would be more easily understood if 
arranged in table form. 


TERM 

UNIT 

MEASURING-INSTRUMENT 

Electromotive force \ 
Potential ) 

Volt 

Voltmeter 

Current 

\ Coulomb 
( Ampere 

Ammeter 

Resistance 

Ohm 

j Wheatstone Bridge 
(Ohmmeter 

Work 

\ Watt 
( Kilowatt 

Wattmeter 


Now that we fully understand the flow of current over 
a wire and just how its progress is opposed by resistance, 
let us see what this has to do with electric heating. 

Resistance is really an opposing force which has to be 
overcome before the electric current will flow. In 

148 


over- 











ELECTRIC RADIATOR 



















HARPER’S EVERY-DAY ELECTRICITY 


coming this resistance some of the electrical energy is 
changed into heat-energy. This is the secret of all electric 
heating-devices. 

Naturally, the first question is how does this wonderful 
transformation take place? Rub a coin on the carpet. It 
will soon become too hot to hold. This is because some of 
the mechanical energy, represented by the motion of your 
arm, is changed to heat-energy in overcoming the friction 
between the coin and the carpet. This demonstrates that 
in overcoming friction mechanical energy is changed to heat- 
energy. 

Phis process is almost exactly duplicated in the electric 
wire. In overcoming the resistance of the conductor some 
of the electrical energy is changed to heat-energy. Perhaps 
the molecules composing the metal are rudely pushed aside 
by the electric current, which travels at terrific speed. This 
increases the vibration of the molecules. Heat being nothing 
more or less than the increased vibration of molecules com¬ 
posing matter, the wire soon gets hot. 

The greater the length of a conductor the greater the 
resistance. The greater the cross-section of a conductor 
the less the resistance, because in the latter case the electrical 
path is larger, offering more room for the passage of the 
current. If it has to crowd over a fine wire the resistance 
is increased. 

It is easy enough to measure the resistance of any con¬ 
ductor. Instruments are made for this very purpose; they 
will be described in succeeding chapters. A 16-candle- 
power incandescent lamp has a resistance of 500 ohms when 
cold and 250 ohms when hot. The resistance of 1,000 feet 
of No. 10 B. & S. gage copper wire is one ohm. A stick of 
graphite 10 inches long and }/ A inch in diameter has a re¬ 
sistance of about 7,000,000 ohms. The resistance of the 

150 


RESISTANCE 


human body is anywhere from 1,000 to 10,000 ohms, de¬ 
pending upon the person. 

1 he resistance of various metals is best shown in the 
following table. 

SPECIFIC RESISTANCE OF METALLIC WIRES 


MATERIAL 

RESISTANCE 

IN OHMS AT 
O 0 C. OF WIRE 

I FOOT LONG, 
.OOI INCH IN 

DIAMETER 

Silver, annealed. 

8.781 

9-538 

9-529 

9.741 

12.56 

12.78 

17.48 

33-76 

54-35 

58.31 

74-78 

79.29 

115 -1 

213.1 

787-5 

565-9 

125-7 

65.21 

Silver, hard-drawn. 

Copper, annealed. 

Copper, hard-drawn. 

Gold, annealed. 

Gold, hard-drawn. 

Aluminum, annealed. 

Zinc, pressed. 

Platinum, annealed. 

Iron, annealed. 

Nickel, annealed. 

Tin, pressed. 

Lead, pressed. 

Antimony, pressed. 

Bismuth, pressed. 

Mercury, pressed. 

German silver. 

Gold-silver (2 parts gold, 1 part silver by weight). 

Although it was known for a long time that electricity 
could be changed into heat, it was not until recently that 
electrical heating-devices were manufactured. For years 


and years electric heat was but a laboratory experiment. 
The trend of electrical invention was to eliminate it as 
much as possible. Over a hundred years ago Davy demon¬ 
strated the tremendous heat of the electric arc. Since then 
the electric furnace has been developed, which will produce 
a temperature of 3,500° Centigrade, twice that of any fuel- 

151 



























HARPER’S EVERY-DAY ELECTRICITY 

furnace. The electric furnace is now in common use in the 
smelting of refractory ores and for other purposes. 

James Prescott Joule, of England, was the first to experi¬ 
ment with electric heat. He determined that 77 $ f° ot> 



ELECTRIC COFFEE-POT DISSEMBLED 


pounds of work would raise the temperature of one pound 
of water 1° Fahrenheit. This is the British thermal unit 
now officially used for measuring heat and abbreviated 

B. T. U. 

By using the proper size of resistance-wire and the proper 
amount of electricity any degree of heat may be produced 
at will. You can graduate the temperature from just 
enough to warm a heating-pad to the carbon melting-temper¬ 
atures of the electric furnace. The rate at which this 
heat is produced is directly proportional to the product of 
the resistance in ohms of the resister and the square of the 
current in amperes. 

For moderate temperatures the resister consists of a long 
thin wire or a flat ribbon through which the electricity is 
made to pass. For high temperatures large resisters are 

152 







RESISTANCE 


necessary. As this makes the resistance low, only low 
voltages (5 to 10 volts) are used, and therefore the amperage 
is high. 

hor electric heating and cooking the resister usually con¬ 
sists of a long cod, or wire, or its equivalent, in the shape 
of a flat metal stamping, concealed and carefully insulated 
within the device itself. 

These heating-elements are designed to give a uniform 
temperature and to conduct the heat rapidly and evenly 
to the points to be heated. Every precaution is taken to 
prevent the loss of heat by radiation. While the heating- 
element forms a part of the device to be heated this unit is 
made so it can be readily detached and replaced if necessary. 



CARTRIDGE HEATING-UNIT 




STAMPED-LEAF HEATING-UNIT 



SPIRAL-COIL HEATING-UNIT 


INCLOSED-DISK HEATING-UNIT 


Where the heating-device takes 500 watts or less the 
ordinary lamp-socket may be used as a source of current. 
Where a greater amount of current is required a special heating- 
circuit must he installed. Any attempt to draw more than 
500 to 600 watts over the electric-light wires will blow the 
protective fuse. When the fuse blows it is a sure sign that 
an excess of current has tried to flow over the wire. The 

i53 





proximate cost per hour where electricity can be had for five 
cents a kilowatt-hour, the usual heating and cooking rate. 

Experience has shown that 300 watt-hours per meal per 
person is a liberal allowance for electric cooking; or in a 
family of five four kilowatt-hours per day is an average. 

Electric heating is also extensive^ used in industrial work 
of all kinds. It is used to heat the tools in book-binderies and 
hat-factories, it is used in candy-manufacturing, electrotyp¬ 
ing, for glue-pots, soldering-irons, shoe-stamping machinery, 
branding-irons, for welding, tempering, annealing, and in 
other ways too numerous to mention. 

154 


HARPER’S EVERY-DAY ELECTRICITY 

blowing of a fuse is always a danger-signal and should not go 
unheeded. 

The table on the following page gives the watt-consumption 
of various household electric heating-devices and their ap- 


TOASTER 


FLATIRON 


DISK STOVE 












RESISTANCE 


APPARATUS 


Broilers, 3 heats. 

Chafing-dishes, 3 heats. 

Cigar-lighters. 

Coffee-percolators for 6-in. stove. . . . 

Coil-heaters. 

Corn-poppers.. 

Curling-iron heaters. 

Double boilers for 6-in., 3-heat stove. . 

Flatiron (domestic size), 3 lbs. 

Flatiron (domestic size), 4 lbs. 

Flatiron (domestic size), 5 lbs. 

Flatiron (domestic size), 6 lbs. 

Flatiron (domestic size), 7.5 lbs. 

Flatiron (domestic size), 9 lbs. 

Foot-warmers. 

Frying-kettles, 8-in. diameter. 

Griddle-cake cookers, 9 ins. by 12 ins., 

3 heats. 

Griddle-cake cookers, 12 ins. by 18 

ins., 3 heats. 

Heating-pads. 

Instantaneous-flow water-heaters. . . . 
Kitchenettes (complete), average.... 

Nursery milk-warmers. 

Ornamental stoves. 

Ovens.. 

Plate-warmers. 

Radiators. 

Ranges, 3 heats, 4 to 6 people. 

Ranges, 3 heats, 6 to 12 people. 

Ranges, 3 heats, 12 to 20 people. 

Shaving-mugs... 

Stoves (plain), 4.5 ins., 3 heats. 

Stoves (plain), 6 ins., 3 heats. 

Stoves (plain), 7 ins., 3 heats. 

Stoves (plain), 8 ins., 3 heats. 

Stoves (plain), 10 ins., 3 heats. 

Stoves (plain), 12 ins., 3 heats. 

Stove, traveler’s. 

Toasters, 9 ins. by 12 ins., 3 heats. . 
Toasters, 12 ins. by 18 ins., 3 heats. . 

Urns, 1 gal., 3 heats. 

Urns, 2 gals., 3 heats. 

Urns, 3 gals., 3 heats. 

Urns, 5 gals., 3 heats. 

Waffle-irons, 2 waffles. 

Waffle-irons, 3 waffles. 


WATTS 


300 to 1,200 
200 ‘ ‘ 500 

75 

100“ 440 

110“ 440 

300 
60 

100“ 440 

275 

350 

400 

475 

540 

610 

50“ 400 

825 

330 “ 880 

500“ 1,500 

5 ° 

2,000 

1,500 

450 

250“ 500 

1,200 “ 1,500 
300 

700 ‘ ‘ 6,000 
1,000“ 4,515 
1,100“ 5,250 
2,000“ 7,200 

150 

50“ 220 

100“ 440 

120“ 600 

165“ 825 

275 “ 1,100 
325 “ 1,300 
200 

330“ 880 

500“ 1,500 
110“ 440 

220“ 660 

330“ 1,320 
400“ 1,700 
770 

1,150. 


CENTS PER HOUR 


i -5 

to 

6 

1 

i i 

2-5 

•375 

< 6 


•5 

2.2 

•5 

i i 

2.2 

i -5 



•3 

6 6 


•5 

2.2 


i -37 

i -75 


2.4 

2.7 

3 - 05 

.25 “ 2 

4- 125 


i-7 

( 6 

4-4 

2-5 

i i 

7-5 

•25 



10 



7-5 



2.25 



1-25 

6 ( 

2-5 

6 

< < 

7-5 

i-5 



3-5 

( ( 

30 

5 

6 i 

22 

5-5 

6 6 

26 

10 

< < 

36 

•75 



•25 

i 6 

1.1 

•5 

( 6 

2.2 

.6 

i C 

3 

.82 

C i 

4-125 

i-3 

i ( 

5-5 

1.6 

c i 

6-5 

1 



1.6 

( ( 

4-4 

2-5 

i c 

7-5 

•5 

( c 

2.2 

1.1 

i i 

3-3 

i-3 

i < 

6.6 

2 

( i 

8-5 

3-75 



5-75 




















































Chapter XIV 


ELECTRIC HEATING-DEVICES AND HOW THEY ARE MADE 

G ERMAN-SILVER wire with a very high resistance is 
generally used by amateurs for the resistance in heat¬ 
ing-devices. A few special alloys have been perfected and 
patented which have a greater resistance than German 
silver. They are also available for the amateur. 

A suitable device for testing the heating-properties of 
various materials can be made easily. The inexperienced 
amateur should use battery currents until he has become 
thoroughly familiar with handling higher voltages. Elec¬ 
tric-light voltages, no to 120 volts, are safe, but they are 
not to be trifled with. Twenty-four dry cells will be quite 
enough for experimental purposes, as they will give about 
30 volts if connected up in series. Half this number will do 
in a pinch. A simple testing-standard consists of an in¬ 
sulated base, two insulated standards, and two sliding- 
conductors for holding the wire to be tested (Fig. 1). 

For the low-battery currents the base can be made of 
hard wood, well seasoned, and soaked with varnish. Soak it 
well in shellac-varnish and dry thoroughly before using. 
The base should be about ten inches long, five inches wide, 
and an inch thick. The uprights should be two inches 
square, six inches high, and mortised to fit the base so they 
are placed eight inches apart in the middle of the same. 
The copper conductors should be eight inches long, sawn 

156 


ELECTRIC HEATING-DEVICES 

or split at one end for the admission of the wire to be tested, 
and ringed at the other for proper connection with the 
battery terminals. Bore a hole through the top of each 
wooden standard to admit a piece of porcelain tube such 
as is used to insulate house wiring where it passes through 
floors and ceilings. This will effectively insulate the con¬ 
ductors. The copper rods should be large enough to fit 
snugly in this tube and at the same time admit of being 
shoved back and forth. This device should also be pro¬ 



vided with an indicating-switch if it is to be used on the 
lighting circuit, so the operator will always know when the 
current is on or off. 

This testing device can be used for either battery or 
ordinary lighting current. If the house-lighting current is 
to be used at about no volts the terminals are connected 
to an ordinary desk-lamp cord. This cord consists of two 
insulated wires covered with silk and has a suitable plug 
connection to screw into the lamp-socket. 

With this device a number of different metals can be 
tested. Place a strip of thin sheet lead six inches long and 
a quarter of an inch wide between the “jaws” of the copper 

l $7 






















HARPER’S EVERY-DAY ELECTRICITY 

terminals and turn on the current. In a few minutes it will 
become quite hot and melt. 

Bits of iron wire will become red-hot. Brass and German- 
silver wire will also become hot. It will be noted that the 
finer the wire the quicker and easier it is heated. The re¬ 
sistance of German silver is 18 times that of pure copper. 
No. 24 copper wire has a resistance of 20.9 ohms per pound. 
The same size wire of German silver has a resistance of 
376.2 ohms. Soft steel has 10 times the resistance of copper; 
platinum, 5.7 times; nickel, 7.9; iron, 6.1; and aluminum, 
1.8. 

Wrap some German-silver wire around a lead-pencil to 
form a spiral six inches long, each turn one-eighth inch apart. 
Hold it in place awhile until the wire “sets,” so it will not 
unwind when the pencil is removed. Loop this coil in a 
glass tumbler and arrange between the terminals of the 
heat-testing machine, and we have the first simple heating- 
device (Fig. 2). 

The electrical energy flowing through the wire coil is 
changed by resistance to heat-energy and it will soon raise 
the temperature of the water to the boiling-point. This is 
the principle upon which all heating-devices are constructed. 
With the knowledge of these fundamentals, and knowing 
the value of proper insulation, any common heating and 
cooking device can be made. 

Toy Electric Incubator 

One of the best applications of electric heat is the toy 
electric incubator. This simple device is easily made and 
entirely automatic in operation. A heating-unit, consist¬ 
ing of a coil of German-silver wire, is concealed beneath the 
egg-tray of the machine. With the aid of an electromagnet 

158 


ELECTRIC HEATING-DEVICES 


and a column of mercury the temperature is automatically 
maintained at 104° Fahrenheit, which is the correct hatching- 
temperature. Of course, the eggs have to be turned and 
sprinkled occasionally, as in any other incubator. This 
device is suitable only for experiment and amusement, as 
but a few eggs can be hatched. 

Build a double box fifteen inches high, eight inches wide, 
and eight inches deep. Fit it with a small glass door so the 
eggs can be watched. Arrange a rack, or a shelf of perforated 
wood, six inches from the bottom (Fig. 3). 

In this lower compartment is to be concealed the heating- 
unit, a coil of German-silver wire wound on a porcelain base 



Ba-Hery Line 



Fig. 3 


Fig. 4 


and carefully insulated. This coil can be made by wrapping 
a baking-powder tin can with asbestos paper and winding 
the wire on that. The coils should be one-eighth inch apart. 

This resistance-unit will furnish the necessary heat for the 
experiment. It is best to line this lower compartment with 
asbestos paper. The whole device should be operated where 
there is no danger in case it gets afire, like any other in¬ 
cubator. 

The eggs are placed on the hatching-tray, as shown in the 
illustration, and the device connected to the lighting circuit, 
or to a suitable battery circuit. 

159 





































































HARPER’S EVERY-DAY ELECTRICITY 


This incubator is kept at a constant temperature by a 
novel switching-device. A glass tube containing mercury 
is arranged in the top of the hatching-chamber. Through 
the cork or cover of this tube protrude two platinum wires 
which are connected to a battery circuit and operate an 
electromagnet. The manner of installing this device is best 
shown in Fig. 4. 

Whenever the temperature of the hatching-chamber 
exceeds 104° the mercury rises and makes a connection 
between the platinum points. This energizes the electro¬ 
magnet, which raises the armature and “breaks” the circuit 
to the heating-unit. When the chamber cools sufficiently 
the mercury drops down in the tube, breaking the circuit to 
the electromagnet, and closing the circuit to the heating-unit. 
The size of the heating-unit and the amount of mercury in 
the tube can be determined only by actual experiment. 

Electric Soldering-Iron 

Any ordinary soldering-iron can be made into an electric¬ 
ally heated iron. Wrap the face of the iron with one layer 
of mica. Over this place a layer of one-sixteenth-inch sheet 
asbestos. Now wind twenty-five turns of No. 20 high-re¬ 
sistance wire over the asbestos covering. Cover with a 
layer of mica and wrap another twenty-five turns over this. 
Now arrange the terminals for connection with the leading- 
in wires and cover with a layer of mica and another layer 
of asbestos paper, and the iron is ready to finish (Fig. 5). 

A protective jacket of sheet brass, or a winding of copper 
wire, must be laid over this heating-unit to protect it from 
injury while the tool is being used. The leads are connected 
to insulated wires and brought out through a suitable hole 
bored in the wooden handle and connected to the regulation 
cord and plug for attaching to the electric-light socket. 

160 


ELECTRIC HEATING-DEVICES 


The Electric Cigar-Lighter 

I he electric cigar-lighter consists of a small coil of very 
fine resistance-wire and a suitable base or container. Very 
fine resistance-wire, No. 39, should be used. Wrap this over 
a darning-needle to form a very small coil three inches in 
length. Withdraw the needle and insert a piece of asbestos 
string in its place. Be sure that all the turns of the coil 
are separate from one another one sixteenth of an inch, so 
it won’t short-circuit. This coil should be mounted in a 
circular piece of asbestos board one-half inch thick. Cut 
out a disk of this board one inch in diameter. Groove it with 
a small gouge to form a spiral recess for the resistance-coil. 
Bore a hole at each end of this groove so the terminals of the 
coil can be brought to the back of the disk (Fig. 6). 



Fig. 6 


Fig. 7 



This, when covered with a perforated disk of mica, forms 
the heating-element of the cigar-lighter. To be effective it 
must be mounted in a metal and plaster-of-Paris receptacle. 
11 161 























































HARPER’S EVERY-DAY ELECTRICITY 


The disk is fitted to a circular brass holder, which in turn is 
fastened to a wooden base or handle (Fig. 7). 

The insulated wires are brought through the base to the 
coil terminals and fastened thereto. The brass container is 
filled with plaster-of-Paris and fastened to the base. A 
suitable push-button switch is arranged in the base to turn 
on and off' the current when the lighter is to be used. This 
lighter is suitable for either direct or alternating current at 
no volts. When the button is pushed the coil should heat 
sufficiently to turn a bright cherry red. It should char 
wood through the mica covering. 

Heating the Shaving-Mug 

Hot water is not always convenient for shaving purposes, 
especially in the early morning. In this case a suitable 
electric shaving-mug-heater is very handy. A heater of the 
immersion type—meaning that it is to be immersed in the 
water in the mug—can be made by any boy handy with 
tools. It consists of a suitable insulating-handle, a porcelain 
base, and the necessary resistance-wire. 

Select a piece of porcelain tube, such as is used in house 
wiring, four inches long and free from bad spots, cracks, etc. 
At the hardware store you can get a good heavy screw five 
inches long which will pass through the hole in the porcelain 
tube. The head of this screw should form a suitable base 
for the porcelain tube. If the screw-head is too large it can 
be filed down even with the tube. The handle can be turned 
of hard wood, maple preferred. A small hole is bored to 
admit the threaded end of the screw and to form one terminal 
of the device. Another hole is bored parallel with this for 
the other terminal (Fig. 8). 

About ten feet of No. 24 resistance-wire will be necessary. 

162 


ELECTRIC HEATING-DEVICES 


Solder one end of this to the head of the screw. Wind the 
remainder of the wire on the porcelain tube, taking care that 
the turns are evenly spaced and one-eighth of an inch 
between turns. The winding should be very firm and tight 
to avoid slipping. This end of the resistance-wire is fast¬ 
ened to the other screw terminal in the wooden handle. 
The lead wire of the lamp-cord is brought into the end of the 
base and connected to the terminals, as shown in the pre¬ 
ceding illustration. The handle for this device can be 
turned on a lathe or taken from an old screw-driver or 
file. 

The lamp-cord used for connecting the device with the 
lighting-socket should be about five feet in length, or 
longer if necessary. The other end of the cord is provided 
with a common screw-plug which fits in the lamp-socket in 
place of the lamp. This device takes about 200 watts, and 
is entirely safe for the lighting circuit. 

In using this type of immersion heater care must be taken 
to place it in the shaving-mug before turning in the water, or 
the porcelain will crack. It should never be used with a 
metal mug. Use it only with china or porcelain mugs of 
good insulating qualities. Place the heater in the mug, 
turn in the water, and turn on the “juice.” In one minute 
the water will be hot enough for shaving purposes. Do 
not operate this heater for any length of time unless it is 
immersed in water. If you do it will get too hot and crack 
the porcelain. 

An Electric Toaster 

An electric toaster is somewhat harder to make than the 
simple electric heating-devices described in preceding pages. 
Nevertheless, the amateur can make one with very little 
trouble and expense. Perhaps in this case it will be better 

163 


HARPER’S EVERY-DAY ELECTRICITY 


to show a detailed drawing of the toaster first. In that way 
it will be easy to take up its component parts and describe 
them in detail (Fig. 9). 

The base of this toaster is made of slate, marble, or heavy 
white asbestos board. It can be of hard wood covered with 
asbestos paper, but this is hardly to be recommended. The 
base should be about eight inches long and five inches wide. 
At each corner is fastened, with rivet or bolt, a small cylin¬ 
drical porcelain insulator at least one inch high for the legs. 
The frame is a sheet of copper or brass or even tin, although 
this latter is not so handsome. It is bent into a rectangular 
shape, as shown in the diagram, and fastened to the base with 
small screws or bolts. The heating-element of this toaster 
consists of three flat coils of resistance-wire, about No. 25, 
wound on uprights of heavy mica. The mica strips are sup¬ 
ported in the frame by double cross-pieces of metal, and they 
are notched so as to hold the wire coils without slipping. 
A suitable rack is built up around these coils to protect them 
from the bread while it is being toasted. Another wire 
rack holds the bread in place. When the toast is done it 
can be conveniently stacked on the top of the metal 
frame. 

About fifteen feet of the resistance-wire will be necessary 
for this type of toaster. If it gets too hot it can be readily 
shortened. The terminals of the resistance-wire are brought 
out through the insulating-base to suitable plugs for attach¬ 
ing to the heating-device cord. These cords, as sold in the 
open market, consist of about five feet of heavily insulated 
double wire, to one end of which is attached a screw-plug 
for the lamp-socket and to the other a suitable plug-contact 
for the heating-device terminals. The terminals to the 
toaster should be made to fit the cord you have on hand or 
the one you intend to use. 

164 


ELECTRIC HEATING-DEVICES 


A Serviceable Immersion Heater 

The immersion heater has a hundred uses about the house. 
It is especially useful when hot water is wanted in a hurry at 
night or in case of illness in the family. But an immersion 
heater is harder to make, as it must be water-tight. Select 
a piece of brass pipe four inches long and with an inside 
diameter of about one inch. Cut threads on the inside of 
each end for a distance of a quarter of an inch. For one end 





r“ e 


Trass sKell 



3 

and dluo Insulai 

ion Core drilled and 


- & -tKreadedy^or winding 


Fig. 10 


Fig. 11 











































































































HARPER’S EVERY-DAY ELECTRICITY 


of this tube provide a brass plug threaded to fit and slotted 
with a hack-saw so it can be screwed in place, flush with the 
edge of the tube. Now solder it firmly in place. The other 
end of the tube is also provided with a brass plug, but this 
plug is drilled and threaded for a one-eighth-inch brass 
pipe (Fig. io). 

On the lathe turn a cylinder of any suitable insulating 
and heat-resisting material, such as lava board or any of 
the various compounds manufactured for this purpose. 
The cylinder should be seven-eighths of an inch in diameter, 
or small enough so it will drop inside the brass tube. Drill 
it lengthwise for one terminal wire and slot it for the other 
as shown in the diagram (Fig. n). Place the tube in the 
lathe and thread it twenty-four turns to the inch. In this 
thread wind No. 24 resistance-wire. It will take about 
twenty feet of wire. Lead one end of the wire through the 
hole in the tube and the other through the slot. Splice the 
ends of the resistance-wire to asbestos-covered heat-resisting 
wire. Bring this wire up through the brass tube and screw 
the same in place (Fig. 12). 

Finish off with solder and polish. Now fasten on the 
handle, through which a hole has been bored for the lead- 
wires. An attachment-plug on the end of the cord for con¬ 
necting with the lamp-socket completes the immersion 
heater. 

The Electric Radiator 

An electric radiator can be made of ordinary carbon 
incandescent lamps. These lamps give off fully 95 per cent, 
heat and less than 5 per cent, light. By fitting a hard¬ 
wood base with receptacles for ten of these lamps, connected 
in multiple, and arranging a metal hood for the radiation of 
the heat produced, a very good emergency air-heater can be 

166 


ELECTRIC HEATING-DEVICES 


made. 1 he porcelain bases are mounted on a wooden block 
and connected in multiple. When mounting the receptacles 
remember to allow room for the lamp-bulbs which are larger 
than the bases. Otherwise mount as closely as possible. 
Connect the bases so that all the outside connections are on 
one wire and all the inside connections on the other (Fig. 13). 



The last socket is left without a lamp. In this the plug 
is screwed for connecting the lamp with the lighting-socket. 
A metal hood, with suitable holes for the circulation of the 
heated air, is arranged for the heater. The amount of heat 
produced by the electric “stove” can be varied by lessening 
or adding to the number of lamps. 

Of course this device takes plenty of current and is really 
quite expensive. By dipping the lamps in metallic paint 
the heat will radiate from the glass bulbs much faster. 

A more serviceable electric heater can be made by follow¬ 
ing the suggestion in Fig. 14. 

The porcelain tubes are about 18 inches long and wound 
with No. 26 resistance-wire, using about 25 feet to each 
tube. Six of these tubes are arranged side by side in a suit¬ 
able metal receptacle, mounted on an insulated base. This 
heater is suitable for uo-volt circuits and consumes about 
500 watts. 


167 

































HARPER’S EVERY-DAY ELECTRICITY 


Only a few of the many applications and possibilities of 
electric heat are enumerated above. The imagination of 
every amateur will conjure up a dozen and one other things 
equally as interesting and instructive. Boys skilled in the 
use of tools have made good serviceable electric flatirons, 
electric cookers, disk stoves, electric radiators, electric 
coffee-pots, and many other applications. 

It is freely predicted by men who ought to know that 
when our coal-supply is exhausted electric heat produced by 
water-power will keep us warm and cook our food, unless 
some other and cheaper form of heat is discovered in the 
mean time. 


Chapter XV 


GENERATING ELECTRICITY BY MECHANICAL POWER 

T HE electricity used to light buildings and streets, to 
drive trolley-cars and motors, for the electrification of 
railroads, etc., is produced by large mechanical generators, 
or dynamos, driven by steam-engines or water-wheels. 

A generator is a machine to produce electrical energy. At 
first thought, after a careful study of the chemical battery, 
this would seem quite impossible. Indeed, it was so con¬ 
sidered up to the very day in 1831 when Michael Faraday 
demonstrated to the contrary. The dynamo, a device of iron 
and copper, actually generates an electric current. For this 
reason it is better known to-day as a generator. The word 
dynamo , once in good usage, is now all but obsolete in the 
great electrical industry. 

Electromagnetic Induction 

In all mechanical generators electricity is produced by a 
process called induction. Induction is hard to grasp. It 
means “the production of magnetization, or electrification, 
in a body by the mere proximity of magnetized or electrified 
bodies.” In other words, if a piece of soft iron is held near a 
powerful magnet, although not touching it in any way, it 
will become magnetized by the influence of the rays issuing 
from the magnet (Fig. 1). 


169 


HARPER’S EVERY-DAY ELECTRICITY 


To fully understand induction it will be necessary to con¬ 
duct a few simple experiments with this new force. 

Hold a compass near a magnet and the needle will be 
violently agitated. It will persist in pointing toward the 
magnet, regardless of the earth’s magnetic poles. Even 
though the compass be held some distance away from the 
magnet it will be visibly affected. This proves that the 





magnetic influence extends out into the air for a considerable 
distance around every magnet. A magnet is supposed to be 
quite surrounded with these invisible rays called lines of 
force , or magnetic rays. 

A bit of soft iron brought within the influence of these 
rays, yet not touching the magnet, will become magnetized. 

170 




























GENERATING ELECTRICITY 


You can easily prove this. The soft iron by itself will not 
attract iron filings. Suspend it before the poles of a good 
horseshoe-magnet, and it will attract the iron filings. When 
the magnet is taken away from the immediate neighborhood 
of the soft iron this magnetism ceases. This is because soft 
iron, while easily magnetized, loses its magnetism just as 
easily. When suspended before the poles of the magnet 
the soft iron becomes magnetic by induction. 

It will pay to stop and investigate these mysterious rays 
just a little. The lines of force in the magnetic field are 
quite invisible. They surround every magnet, being of 
greater density at the poles. They flow out of the north 
pole and into the south pole (Fig. 2). 

These lines of force can be easily demonstrated with a 
common magnet, a thin piece of cardboard, and some fine 
iron filings. Place the cardboard over the poles of the 
magnet and dust with the iron filings. Tap the paper 
lightly with the finger. This will assist the filings to arrange 
themselves (Fig. 3). 

It will be seen that the iron filings have arranged them¬ 
selves in distinct curved lines. These lines represent the 
invisible lines of force ever flowing through the air between 
the poles of the magnet. 

Magnetic rays, or lines of force, extend around every 
conductor of electricity, every wire carrying a current, as 
well as every magnet (Fig. 4). 

Inducing an Electric Current 

Many years ago Faraday demonstrated that if a bit of 
copper wire is passed across the lines of force, between the 
poles of a magnet, so as to cut the rays at right angles, a 
current of electricity will be generated in the wire (Fig. 5). 

171 


HARPER’S EVERY-DAY ELECTRICITY 


To try this experiment a little device called a detector 
(because it is used to “detect” weak electrical currents) is 
quite necessary. An ordinary compass can be utilized for 
this work. Place the loop of copper wire so a portion of it 
lays across the face of the compass immediately above and 



Fig. 6 Fig. 7 


parallel to the compass-needle. Now if a weak current of 
electricity passes over this wire the compass-needle will 
swing out at right angles to the wire, pointing east and west 
instead of north and south. This is owing to one of the 
natural laws of magnetism that similar magnetic poles 
repel each other, and dissimilar poles attract each other 

(Fig. 6). 

Pass the wire down between the poles of a good horseshoe- 
magnet, watching the compass the while. It will be seen 
that the needle swings at right angles to the wire, as stated 
above, evidencing that a current of electricity has been 
generated in the wire. 


172 








































GENERATING ELECTRICITY 


This experiment can be made plainer with a suitable 
coil, or spool, of insulated copper wire. Connect the coil 
terminals to a galvanometer, or to a compass detector, as 
described above. Now thrust the north pole of a good bar- 
magnet into the center of the coil. Instantly the compass- 
needle will be deflected, proving that a current of electricity 
has been induced in the wire loops of the coil. You will 
notice that this current flows only when the magnet is in motion. 
When the magnet is at rest in the coil there is no flow of 
electricity. When it is extracted from the coil another 
current is generated, but the needle shows that it flows in the 
opposite direction. The current flows one way through the 
coil when the magnet is inserted and the opposite way when 
it is withdrawn. If the magnet is moved very slowly no 
current will result. The faster it is moved the greater the 
current induced (Fig. 7). 

It makes no difference whether the coil is moved over the 
magnet or the magnet thrust into the coil, the result is 
exactly the same. 

Perhaps the best example of an induced current is to be 
found in the operation of an induction-coil. This coil is 
really a small transformer. It consists of a primary coil , 
through which flows a current of electricity from a battery. 
Wrapped around this primary coil, but effectively insulated 
from it, is the secondary coif consisting of many turns of 
very fine insulated wire. We know that no current can 
flow from the primary coil to the secondary coil owing to the 
heavy insulation. And yet when a pulsating current of low 
voltage and high amperage is sent through this primary coil 
it induces a current to flow in the windings of the secondary 
coil. This secondary current is of high voltage and low 
amperage. The device cannot increase the amount of power, 
although it does increase its pressure, or voltage. 

173 


HARPER’S EVERY-DAY ELECTRICITY 


Just how this secondary current is induced we will not 
attempt to explain. It might satisfy an idle curiosity, but 
would be of no particular value to the work in hand. Let us 
accept as a fact, amply proven by experiment, that whenever 
a conductor is moved within the lines of force in a magnetic 
field a current of electricity is produced. The strength of 
; this current depends upon the speed of the conductor and 
the density of the magnetic field. 

This is the whole story of the electric generator. 

When you pass a wire down between the poles of a magnet 
electricity is produced. In reality some of the mechanical 
energy of your body has been changed to electrical energy. 
If we use a steam-engine or a water-wheel to whirl a number 
of these loops in a magnetic field we can change any amount 
of mechanical energy into electrical energy. The electricity 
produced in this way does not differ from that produced by 
chemical batteries. It can be used for light, power, heat, 
etc. To force these loops across the lines of magnetic force 
requires considerable power, however, as the attraction of 
the powerful magnets has to be overcome. There is also 
some loss of energy in friction, eddy currents, etc. For 
every 746 watts, or one horse-power, of electrical energy 
produced we have to use somewhat over one horse-power of 
mechanical energy. 

To follow the path of the electric current produced by the 
mechanical generator we must take up a single loop of the 
conductive wire from the armature, or rotating part (Fig. 8). 

When this loop of copper wire is stationary no current 
flows. When it first begins to move its motion is parallel 
with the lines of magnetic force flowing between the magnetic 
poles, as shown by the illustration. This also results in no 
flow of current. But when the top of the loop begins to 
cut down and across the lines of force and the bottom of the 

174 


GENERATING ELECTRICITY 


loop begins to cut up and across the lines a current begins 
to flow in the wire conductor. This current continues to 
flow as long as the loop is cutting the lines of force at right 
angles. When the conductor again parallels these lines 
the current stops. This completes a half-revolution of the 
loop. Now the top of the loop, being at the bottom of the 
held, begins to cut the lines of force in an upward direction. 
The bottom of the loop, now at the top, cuts them on the 
other side in a downward motion. The result is another 
current in the loop, but it flows in the opposite direction. 

Thus, with every complete rotation of the wire loop two 
currents of electricity are produced, one flowing to the right 
and the other to the left. The electricity, surging first one 
way and then the other, is known as alternating current. 
The electromotive force generated in the armature-wind¬ 
ings of any generator is alternating in character. If direct 




current is desired this alternating current must be rectified , 
or sent out in one direction, by a device called a commutator. 

If the armature loops are connected at each terminal to 
individual rings insulated from each other and the current 

175 



















HARPER’S EVERY-DAY ELECTRICITY 

is taken from these rings by sliding-contacts an alternating 
current will flow over the line. If a split ring is used and the 
loop terminals are connected to alternate sections of the 
ring a direct current will result. This direct current will 
be pulsating in character. It will not flow even and steady 
like a stream of water. 

Now that we understand how the generator creates an 
electric current, we will take one of the machines apart and 
see how it is made. Let us first consider the side and end 
elevation of a simple direct-current generator (Fig. 9). 

This dynamo can be divided into three essential parts. 
The first of these is the magnetic poles (MP) upon which the 
exciting-coils (EC) of insulated wire are wound to produce 
the electromagnets. It is the function of these coils to 
supply the field with its magnetism. The iron frame of the 
machine acts as the yoke to connect the pole-pieces of the 
magnets. The design of the soft-iron pole-pieces is such as 
to cause the magnetic lines of force to pass straight across 
from pole to pole with considerable density. 

The second essential part of the machine is the armature 
(< a ). This consists of a number of copper loops systematic¬ 
ally arranged over a soft-iron core. When this armature is 
rotated in the magnetic field these loops of copper wire cut 
the lines of force at right angles and produce the flow of 
current. These copper wires are connected to the terminals 
of the armature, which is known as the commutator (c). The 
wires of the armature are mounted on a heavy iron shaft so 
they can be rotated in the field. This shaft also performs 
the same service as a “keeper” to a horseshoe-magnet. 

The third important part of the machine is the commu¬ 
tator. This is a small device affixed to one end of the 
armature shaft designed to collect the current from the 
armature coils and send it out over the circuit. The 

176 


GENERATING ELECTRICITY 



DIRECT-CURRENT GENERATOR 



DISSEMBLED VIEW OF DIRECT-CURRENT GENERATOR 

commutator (c) is made of copper strips which are insu¬ 
lated from each other by sheets of mica or other insulating- 
material. Each end of each wire in the armature is con¬ 
nected to one of these copper bars in the commutator. The 
current is picked off' of these commutator - bars by the 
12 177 








HARPER’S EVERY-DAY ELECTRICITY 

brushes , or sliding-contacts, and carried away to the external 
circuit. 

There is a simple rule which, if remembered, will enable 
any one to understand the action of a generator. If the 
index finger of the right hand is extended along the armature 
coil, with the thumb and second fingers at right angles to it, 
it will show the direction of the current generated, the 
direction of the magnetic lines, and the direction of motion 
(Fig. io). 

It is quite necessary to have a number of such loops in 
the armature in order to have enough potential difference 
for practical work. By simply increasing or decreasing the 
speed of the armature the electromotive force, or potential 
difference, or voltage, is increased or decreased. The 
electromotive force of the generator depends upon the 
number of conductors cutting across the lines of force, the 
speed of the armature, and the density of the field. All 
generators are built to give a certain amount of current 
when run at a certain speed. 

The capacity of a generator is usually given in kilowatts, 
inscribed on the name-plate, along with its voltage. To 
find the horse-power you must multiply the kilowatts by 
1,000, to reduce it to watts, and divide by 746, the number 
of watts equaling one horse-power. A generator rated at 
3 kilowatts is equal to 3x1,000, or 3,000 watts -j- 746, or 
about 4 horse-power. 

Different Kinds of Generators 

Electric generators are roughly divided into two kinds— 
the alternating-current generator and the direct-current 
generator. Of these the alternating-current machine is 
best known and generally used. 

178 


GENERATING ELECTRICITY 


There are a number of different designs of both alternating 
and direct current generators. 

The well-known direct-current machines may be two-pole, 
four-pole, six-pole, and even more. The field-coils may be 
excited from an independent source, by shunt connection 
with the circuit, or by series or compound connection. 
The design of direct-current machines varies with the work 
it is expected to do. 

Although the current in the armature of a direct-current 
machine is alternating in character, the design of a modern 
alternating-current machine differs materially from the 



STATOR FOR ALTERNATING-CURRENT 
GENERATOR 


direct-current type. The alternating-current generator is 
usually called an alternator. The part that revolves is known 
as the rotor. The frame and part that is stationary is the 
stator. It is the general practice to reverse the order in these 

179 



HARPER’S EVERY-DAY ELECTRICITY 


machines and revolve the “held/’ while the “armature” 
stands still. This is so the armature may be better in¬ 
sulated and not subjected to the centrifugal force of being 
whirled at high speed. 

All generators require power to whirl the armature in the 
magnetic field. The power required is directly propor¬ 
tional to the current-flow and the voltage. The power 
required depends upon the amount of work, represented in 
kilowatts, the generator has to do, plus a small loss in friction 
and heat. This loss is small, as the efficiency of a good 
generator is often over 95 per cent. If 100 horse-power is 
used to drive the machine, 95 horse-power of electrical 
energy is available for use. 


Chapter XVI 

CONSTRUCTION DETAILS OF A SMALL GENERATOR 

T HE smallest generator which can be made on the work¬ 
bench is but a loop of copper wire whirled between 
the poles of a good horseshoe-magnet. This device is but 
a toy. The galvanometer or compass detector will show 
that it actually produces a pulsating current of electricity 

(Fig. i). 

The loop of copper wire is mounted on a small wooden 
shaft, which effectively insulates it. The ends of the loop 
are brought out to a split brass ring insulated from the 
shaft. The wooden shaft is supported by a suitable frame 
and whirled by the small crank. A small pulley affixed to 
the shaft and belted to a large pulley, which is driven by a 
crank, will give greater speed. 

Making a Magnet 

Perhaps you will have to make this magnet. If so select a 
piece of tool-steel an inch and a quarter wide and an eighth 
of an inch thick. This steel should be nine inches long so 
that when it is bent in U-shape it will form a horseshoe 
four inches high. To bend this piece of steel it will have 
to be heated. To retemper, heat it a dull cherry-red and 
plunge quickly into cold water. Test it with a file and when 
it is quite hard it is ready to be magnetized. 

181 


HARPER’S EVERY-DAY ELECTRICITY 


To magnetize this bit of steel lay it face down, with the 
ends touching the poles of a good horseshoe-magnet. Stroke 
it gently with the soft iron “keeper” of the magnet. Rub 
both with the keeper, beginning at the curved end of the 
magnet and rubbing toward the curved end of the steel. 
Be careful to rub the steel always in one direction. After 
twenty strokes turn magnet and steel and rub an equal 
number of times on the other side in the same way. Be 
careful in turning to keep the same poles facing (Fig. 2). 



Fig. 1 


*— 




</> 

u 

<D 


( 


1 

p 

<0 

z 


_ 

<Steel 

M a « 




Fig. 2 



Fig. 3 


It is a simple matter to mount this magnet in a wooden 
frame and arrange the armature shaft and loop. The loop 
should not touch the sides of the magnet. It should pass 
very near it, however. The greatest difficulty will be 
found to connect the ends of the loop with the commutator^ 
rings. This is best shown in a diagram (Fig. 3). 

When the armature shaft is whirled rapidly in the magnetic 
field so the copper loop cuts the lines of force flowing from 
pole to pole a current of electricity will be generated. The 
compass detector will show the extent and direction of this 
current. 

This device is but a toy. It is possible to clamp together 
a number of similar horseshoe-magnets and arrange a drum- 

182 











































DETAILS OF A SMALL GENERATOR 

armature so it can be whirled rapidly between the poles. 
In this way a considerable flow of current can be produced. 
This is really a magneto similar to those used for ignition 
and lighting purposes on automobiles (Fig. 4). 

Building a Generator 

In constructing a small generator the amateur will 
always have more or less trouble with the frame and 



Fig. 4 


MAGNETO SUCH AS IS USED FOR IGNITION PURPOSES ON AN AUTOMOBILE 

pole-pieces. The frame must be of soft iron. For large- 
size machines this frame must be cast. For smaller ma¬ 
chines it can be made in sections, bolted together. The 
frame of a small generator of this latter type consists of the 
electromagnets, the yoke, and the pole-pieces (Fig. 5). 

The electromagnets E-E, consisting of spools of insulated 

183 










HARPER’S EVERY-DAY ELECTRICITY 


copper wire, are slipped on the iron cores C-C and are held 
together by the yoke Y. The pole-pieces P—P, which direct 
the lines of force between the poles, can be easily and 
quickly sawed from a piece of iron pipe. Select a piece of 
pipe two inches in diameter and as wide as desired, usually 



about one and one-half inches, and drill it exactly in the 
middle so it can be fastened to the poles of the electromagnet, 
as shown in the illustration. These drill-holes should be 
tapped or threaded for the screws which hold them in place- 
Now with a hack-saw cut out a section of the iron pipe as 
shown above. Remove an inch at top and bottom. When 
these plates are firmly fastened to the poles of the elec¬ 
tromagnet they form excellent pole-pieces for the revolving 
armature. 

Adjusting the Electromagnet 

There is but one possible error in adjusting the electro¬ 
magnet coils. The wire turns of the coils must be always in 
the same direction, otherwise the spools will neutralize each 
other and no magnetism will result. Be sure the spools are 
wound in the same direction. In winding the spools use fine, 
well-insulated copper wire. Bring the ends of the wire out 
to suitable terminals for connection with a battery for 
energizing the magnet. 


184 















































































DETAILS OF A SMALL GENERATOR 


Frames of Cast Iron 

For all practical generators of 25 watts and larger the 
frame should be of cast iron. A number of different styles 
of generator frames suitable for the amateur to make are 
shown in Fig. 6. 

There is quite a trick in making patterns for the foundry- 
man. Bear in mind that a “flask,” or the frame in which 
the casting is made, consists of two parts. One-half of 
the impression is made in the molding-sand in each half 
of this frame. Patterns should be made of soft wood. 
White pine is right. For the reason given above all pat¬ 
terns should taper slightly from the “parting line” where 
the flask opens. This is so the pattern can be easily re¬ 
moved from the sand without spoiling the impression. On 
all large patterns a little surplus has to be allowed for 
shrinkage. But for small castings, such as the amateur 
will require, this is not necessary. However, one-sixteenth 
of an inch should be allowed if the casting is to be machined 
or finished. All sharp corners should be slightly rounded, as 
the sand will not take a sharp edge. A small generator of 
from 25 to 50 watts will require a casting five inches wide, 
three inches thick, and ten inches high. 

Making the Armature 

Making the frame is simplicity itself compared with 
making the armature. Whether the frame is made of sep¬ 
arate pieces bolted together, cast in a whole block, or built 
up out of pieces of sheet iron cut in the proper shape, makes 
little difference. The effect will be much the same. But 
special attention must be paid to the armature, or no current 
will result. 

The armature must consist of a suitable shaft, so it can 

185 


HARPER’S EVERY-DAY ELECTRICITY 


be rotated, and carefully made slots for the conductor wires. 
The size of the armature will depend, naturally, on the size 
of the generator frame and the distance between the pole- 
pieces. So no attempt will be made to give dimensions in 
describing the armature. Whether big or little, they are 
made the same way (Fig. 7). 

The armature shaft is made of soft iron. ’It can be 
easily worked in a lathe. Being so small, metal cutting-tools 
are not necessary. The rough shaft can be whirled in the 
foot-lathe and cut with a file. This is easier and better 
than filing and assures an accurate, well-centered shaft. 
It is not so easy to slot the armature. This can be done 
best with a coarse hack-saw. It can be done with a narrow 
file, but it is hard work. By all means use a saw if you can. 

Winding the Armature 

The armature as depicted above is wound with four loops 
of insulated copper wire. These loops of wire are just long 
enough to extend entirely around the armature for connec¬ 
tion with the commutator segments as shown in Fig. 8. 

The coils of wire must fit tightly in the grooves in the 
armature. Heavy shellac varnish will help to hold them in 
place. If they are loose they will certainly fly out when the 
armature is whirled at high speed. Be careful in assembling 
the coils not to cut the insulation where the wire bends 
sharply over the edges of the slots. Each end of the copper 
loop should be soldered to its particular section of the 
commutator. These sections should be opposite each other 
on the shaft. 

The Commutator 

The commutator is nothing more or less than a split ring 
fastened to the armature shaft. But it must be insulated 

186 


DETAILS OF A SMALL GENERATOR 

from the shaft, and each section must be insulated from 
every other section (Fig. 9). 

This commutator consists of eight sections. The problem 
of insulating them one from the other is easy enough for 
large machines. Then the sections are large enough to be 
handled. For small machines this is not so easy. 

The best way to make a small commutator is to cut a 
ring of heavy brass a little larger than the armature shaft 
upon which it is to be mounted. Mount this on a wooden 



Fig. 8 Fig- 10 

187 












HARPER’S EVERY-DAY ELECTRICITY 


shaft so it can be handled and worked. Mark this brass 
ring into its respective sections, using a compass and awl. 
Saw into each mark, but be careful not to saw way through. 
Gradually work entirely around the ring until every section 
is sawed nearly through. Then it will be an easy matter to 
cut them out. If the ring is split first the sections will 
become harder and harder to work. 

These sections are soldered to the armature loops as de¬ 
scribed above. The shaft is covered with shellac where the 
commutator is supposed to fit. While the varnish is still 
wet slip on a thin sleeve of mica. This will insulate the 
brass commutator from the shaft. The commutator sec¬ 
tions are held in place by hard-rubber rings, or rings of any 
good insulating-material, or even with rubber bands. Each 
section must now be insulated from its neighbor with a tiny 
strip of mica or with sealing-wax. 

The commutator-brushes, which pick the current from the 
sections and send it out over the line, always in one direction, 
are very easily made. They are merely strips of spring- 
brass fastened to an insulating-base and arranged to press 
lightly on opposite sides of the revolving commutator 
(Fig. io). 

One brush collects current from the topmost section of the 
commutator and the other presses against the bottom section 
as shown in the illustration. 

The current collected from the commutator by the 
brushes is sent out over the circuit in exactly the same 
manner as current produced by a chemical battery, except 
it is of a pulsating nature. 

Exciting the Field-Coils 

In order to generate current the field-coils, or the electro¬ 
magnet, must be excited. A current of electricity must be 

188 


DETAILS OF A SMALL GENERATOR 


sent through the insulated wire of the coils or it will not 
become magnetic. For all small generators a separate sup¬ 
ply of current from an ordinary dry-battery cell is best. 



B. Series-wound armature and field. 

C. Shunt-wound armature and field. 

D. Compound-wound armature and field. 

Fig. 11 

For larger generators the “field” may be placed in series 
with the external circuit, or a portion of the current pro¬ 
duced may be shunted through the field-coils (Fig. n). 

Power for the Small Generator 

Hand-power is all right for toy generators. As these 
must be revolved at high speed, a belt and pulley are neces¬ 
sary. Larger machines must be operated by some form of 
mechanical power. A small water-motor which can be 
operated on the kitchen faucet makes an ideal source of 
cheap power. A small home-made windmill can also be 
used, or even the gasolene-engine, if the generator is quite 
large. 

To drive a generator with an engine it is necessary to be 

189 




































































































































HARPER’S EVERY-DAY ELECTRICITY 


able to figure the speed of pulleys, shafts, etc. Generators 
must be driven at high speed, from 1,500 to 2,500 revolutions 
per minute. In order to determine the speed of a pulley 
multiply the speed of the “driver” by its diameter in inches 
and divide by the diameter of the “driven.” Thus a pulley 
two inches in diameter, revolving 1,800 times a minute, will 
drive a 10-inch pulley at 360 revolutions per minute. 


1,800 X 2 = 3,600 -r-10 = 360 R. P. M. 



Small generators can 
be used to light min¬ 
iature lamps, to oper¬ 
ate small motors, or to 
experiment with stor¬ 
age batteries, electro¬ 
plating, etc. 


Alternating - Current 
Generators 

By simply placing 
contact - rings on the 
armature shaft the 
generators mentioned 
above will produce al¬ 
ternating current. These contact-rings must be insulated 
from the shaft and from each other. They can be made of 
brass and insulated with strips of mica, or even with hard 
rubber (Fig. 12). 



/ 
















Chapter XVII 


THE DIFFERENCE BETWEEN DIRECT AND ALTERNATING 

CURRENT 

D IRECT current flows always in one direction. 

Alternating current pulsates back and forth over 
the line, first one way and then the other. 

At first only direct current was desired. Then all genera¬ 
tors were made with split-ring commutators so the alternating 
current of the armature was always sent out to the external 
circuit in one direction or in a continuous stream. 

As the use of electricity extended it was soon discovered 
that alternating current had many inherent advantages 
over direct current. It was easier to generate alternating 
current in higher voltages. It could be more easily and 
cheaply transmitted, because the voltage could be raised or 
lowered at will. For these reasons and others alternating 
current is now almost entirely used for light and power except 
in special instances. For the most part, our trolley-lines 
still use direct current. A number of steam-railroads have 
been electrified to use direct current. In a few of the larger 
cities direct-current light and power systems are still in use. 
And, of course, direct current has to be used in charging 
storage batteries. 

Inasmuch as alternating current is the kind we all use, 
speaking generally, it is well to stop and give this our serious 
consideration. 

191 


HARPER’S EVERY-DAY ELECTRICITY 


An alternating current, according to the definition, is one 
that changes its value, and reverses in direction at certain 
regular intervals. 

Now let us see if we cannot understand, this better by 
comparing it with water in a pipe (Fig. i). 

Here we have a cylinder provided with a piston and filled 
with water. Connected to each end of the cylinder is an end¬ 
less pipe system. When the piston P is moved toward the 
other end of the cylinder it forces a certain quantity of 
water through the pipe circuit. This water flows back into 
the cylinder behind the piston. When the motion of the 
piston is reversed and it is moved back an equal amount of 
water is forced through the pipe system in the other direction. 



Fig. 1 





And so, as you see, as the piston moves the water flows first 
one way and then the other through the pipe. 

This is exactly what happens on an alternating-current 
electric circuit (Fig. 2). 

The current leaves the generator in the direction of the 
arrows and flows over the wire circuit and back to the 
generator. As the armature of the generator turns, corre- 

192 


























DIRECT AND ALTERNATING CURRENT 

sponding to the movement of the piston in thewater-cylinder, 
the current leaves the generator from the other side and 
flows over the circuit in the opposite direction. 

Referring again to the single armature loop cutting the 
invisible lines of force between two magnetic poles, it will 
be remembered that at the first half-revolution of the loop 
a current is gradually built up to maximum, flowing from 
the right to the left, and then gradually drops back to 
minimum as the loop begins to parallel the lines of force. 
At the second half of the revolution a similar current is pro¬ 
duced, but it flows from left to right. This is best illus¬ 
trated by the current curve shown in Fig. 3. 

The flow of current during one half-revolution is called 
an alternation. 

Two alternations, or a complete revolution of the loop, 
is called a cycle. 

The number of cycles passed through in a second is called 
the frequency. 

Of course, there are a number of armature “loops” in a 
modern alternator. When two or more alternating currents 
have the same frequency and pass through their values at 
the same time they are said to be in synchronism or in 
phase. 

For household use alternating current is generated at 
sixty cycles. This is too fast for the human eye to see, even 
if electricity could be seen. An ordinary incandescent lamp 
will not flicker at sixty cycles because the filament does not 
get a chance to cool off between the alternations. For 
power use, for long-distance transmission, and for railway 
service a frequency of twenty-five cycles a second is used. 

A two-phase alternator has two separate windings. 
These are arranged so that the voltage in one is at zero at the 
instant the voltage in the other is at maximum (Fig. 4). 

13 193 


HARPER’S EVERY-DAY ELECTRICITY 


By referring again to the armature loops we can readily see 
how this happens (Fig. 5). 

When the coil A is cutting no lines of force the coil B 
is cutting them at the maximum rate, therefore produces 
maximum voltage when A produces no voltage. 

In the three- P h ase alternator still another series of 
windings, or “loop,” is applied to the armature (Fig. 6). 



The action of the three-phase machine is shown in Fig. 7. 

Let’s see if we have this straight. 

An alternator arranged to give to a two-wire circuit a 
single voltage is called a single-phase machine. An alter¬ 
nator arranged to give two separate and distinct voltages, 
one of which is a maximum when the other is zero, and 
vice versa , as indicated by Fig. 4, is called a two-phase 
machine. An alternator arranged to supply to three wires 
three voltages separated in phase from each other by an 
angle of 120° (Fig. 6) is called a three-phase machine. 

In the alternating circuit not always does the current, 

194 





















DIRECT AND ALTERNATING CURRENT 


or amperage, keep pace with the electromotive force, or 
voltage. When they travel along together they are said to 
be in phase. When the current drops behind the voltage it 
is said to lag. This is shown in Fig. 8. 

These diagrams used to illustrate the salient points of 
this chapter are elementary at best. Perhaps the reader 
will better understand the nature of an alternating generator^ 
or alternator, by referring to the illustration of a modern 
machine shown in detail in Chapter XV. 


Chapter XVIII 



MEASURING ELECTRICITY 


W HEN they first began to sell electrical energy they 
were puzzled to know just how to measure it. In¬ 
asmuch as electricity is an invisible force, traveling at 
terrific speed, with many strange ways peculiar to itself, it 
was not until very recent times that electrical measuring- 
instruments were perfected. 

To find out how much electricity there is we must measure 
the voltage , or pressure, the current-flow, or amperage , and 
the amount of work it will do, or the watts. In addition to 

this a modern power-house 
equipment calls for in¬ 
struments to measure 
power factor, frequency, 
to detect grounds, etc. 

Instruments for meas¬ 
uring current are called 
ammeters. They measure 
the current-flow, or the 
number of amperes. 

Instruments for meas¬ 
uring the electrical pres- 

ammeter sure > or voltage, are called 

voltmeters. 

For measuring the energy of electricity, or the amount of 
work it will do, the watt-hour meter , or the wattmeter , is used. 

196 


MEASURING ELECTRICITY 


Some meters depend upon the action of a magnet or a 
solenoid for the movement of the pointer over the dial. 
Others are but small mo¬ 
tors, chemical cells, static 
devices, etc. 

The simplest of all elec¬ 
trical measuring - instru¬ 
ments is the galvanometer. 

It is only used to register 
the amount of very small 
currents. The galvanom¬ 
eter consists of a small up¬ 
right coil of insulated cop¬ 
per wire provided with 
suitable terminals for con¬ 
necting it in the circuit. 

Inside this coil is mounted a magnetic needle delicately bal¬ 
anced on a very fine strand of silk. Immediately beneath 
this needle is a circular piece of cardboard upon which is 
printed the calibrated scale for reading the instrument 

(Fig. i). 

These instruments are intended for experimental and 
laboratory use. They are employed in measuring very 
small currents, and are of especial value in making experi¬ 
ments. The instrument is “set up” so the needle is balanced 
in the center of the coil, as shown in the illustration. When 
a very small current is sent through the coil the needle 
will be deflected, and its strength can be read on the cali¬ 
brated scale. This instrument also shows the direction of 
the current through the coil. 

Many of the first instruments for measuring electricity 
were of the electrolyte and hot-wire type. The first Edison 
measuring-apparatus was nothing more or less than a 

197 



HARPER’S EVERY-DAY ELECTRICITY 


chemical cell. The weight of metal deposited or of water 
decomposed by a given quantity of electricity is known. 
So the electrolyte cell may be used as a quantity-measuring 
instrument. By taking out the cathode plate and weighing it 
to see how much metal has been deposited upon it by the 
passage of the current the amount of current can be de¬ 
termined. 

The hot-wire meters depend upon a resistance-wire which 
is heated by the passage of the electric current. The 
common type of hot-wire instrument is shown in Fig. 2. 




Fig. 3 


The first ammeters and voltmeters were of the Kelvin 
type, with gravity or spring control. This instrument was 
perfected by Lord Kelvin. Its action is depicted in Fig. 3. 

The soft-iron rod R is drawn into the coil, or solenoid, S, 
in proportion to the current flowing through the line. The 
movement of the rod up and down causes the pointer 
P to play over the scale. The rod R is pulled from the coil 
by the force of gravity acting on the weight W working in 
the oil-cup OC. 

This instrument can be used for either alternating or 

198 






















MEASURING ELECTRICITY 

direct current. The calibration of the dial is determined 
by the number of turns in the solenoid coil. 


The Ammeter 


Th e ammeter is 
constructed along 
the same lines as 
the galvanometer. 
There are a num¬ 
ber of different types 
of these instru¬ 
ments. IntheThom- 



Fig. 4 


son inclined-coil ammeter the coil which carries the current 
is mounted at an angle to the shaft which supports the 

pointer, or indicator. Mounted on 
the shaft is a bundle of iron strips, 
held in position by a spring, so that 
when there is no current in the coil 
its position is parallel with the plane 
of the coil (Fig. 4). 

When a current is sent through 
the coil the iron strips then take up 
a position parallel with the magnet¬ 
ic field. This rotates the shaft and 
moves the pointer. 

The plunger type of ammeter works on the principle of a 
solenoid, or hollow magnetic coil (Fig. 5). 



Fig. 6 





























































































HARPER’S EVERY-DAY ELECTRICITY 


The current is sent through the coil C, which exerts a 
magnetic pull on the soft-iron plunger P. This draws the 
iron rod into the magnetic coil, or solenoid, and causes the 
pointer to move over the magnetic scale. 

The Voltmeter 

The voltmeter is built on the same general principle as the 
ammeter. The principle of the moving-coil voltmeter is 
best shown in Fig. 6. 

To the horseshoe-magnet is fastened two pole-pieces sim¬ 
ilar to a toy motor. To the pointer is affixed a narrow 
rectangular coil of wire which swings on a pivot between 
the pole-pieces of the magnet. Its motion is controlled by 
a bronze hair-spring. The action of the instrument is due 
to the fact that the moving coil when carrying a current 
endeavors to turn into such a position that the lines of force 
it produces will coincide in direction with those flowing 
from the permanent magnet. 

The voltmeter and ammeter are connected to the line as 
shown in Fig. 7. 

The Watt-Hour Meter 

Electricity is sold by the kilowatt-hour. For this reason 
watt-hour meters are necessary. These show the total 
kilowatt-hours consumed in the circuit for a given period of 
time. The wattmeter installed in the home to register the 
amount of electrical energy consumed is really a tiny electric 
motor of the most delicate structure and the best workman¬ 
ship, housed in a little iron-and-glass box. The revolving 
part of the motor is an aluminum disk mounted between two 
electromagnets through which the current to be measured 
is passed. The current in the magnets induces a current in 
the disk, and this current flowing in the field of the electric 


200 


MEASURING ELECTRICITY 


magnets causes the disk to revolve with a speed directly 
proportional to the amount of current that is passing 
through the magnets. With each complete revolution of 
the disk a black band is seen to pass the glass-covered aper¬ 
ture in the face of the meter-box, and a definite number 
of revolutions of the disk indicate that one kilowatt-hour of 
electricity has passed through the meter. 

There are four dials on the face of the meter-box, and the 
disk is geared to them in such a way that when one kilowatt- 
hour passes through the meter the disk revolves a sufficient 
number of times to cause the indicator of the right-hand 
dial to move one-tenth of the distance around its circle. 
That is, if the meter is set at zero the indicator on the right- 
hand dial will move from zero to one in measuring one 
kilowatt-hour of electricity. 

In reading the dial of a meter it is necessary to read the 
number last passed by the pointer. This is important for 
accurate reading. The dial farthest to the right is read 
and the number set down. Then the next dial to the left 
is read and the number is written just to the left of the 
first number, and so on until the four readings have been 
taken and recorded. The numbers are not added together, 
but are read as one whole number just as they stand 
(Fig. 8). 

As an example, suppose the pointer of the left-hand dial 
has just passed four, the hand of the second dial is between 
the one and two, the third is between three and four, and 
the pointer of the fourth or right-hand dial is between two 
and three, then the meter reads four, one, three, two. Four 
thousand one hundred and thirty-two kilowatt-hours have 
passed through it since it started from zero. The right-hand 
dial registers kilowatt-hours singly, the next dial registers 
them by tens, the third by hundreds, and the fourth or left- 

201 


HARPER’S EVERY-DAY ELECTRICITY 


hand dial by thousands. In every case the number printed 
above the dial is the number of units registered by one 
complete revolution of the dial hand. The reading of the 
previous month is subtracted from the new reading and the 
resulting number of kilowatt-hours. If the resident’s rate 
is twelve cents per kilowatt-hour a simple multiplication 
gives the amount of the month’s bill. 

The house meter is usually read every month. The 
meter-reader has a record of what the last reading was. By 


2000 loo 7 o t 



setting down the present reading and subtracting the former 
reading from it he can determine the kilowatt-hours consumed 
in the month— viz.: 

9,568 = Present reading 
9,542 = Former reading 

. 26 = Kilowatts 
. 12 = Rate 

3.12 = Amount of bill 
202 




MEASURING ELECTRICITY 

In reading the meter be sure to watch two dials at the 
same time. Take the meter as shown in Fig. 9. 

In the dial marked 10,000 we see the pointer between 2 
and 3, which means that it did not reach the 3 yet, but to 



make sure we look at the next dial and find the pointer 
between 9 and 10 but not quite reaching the zero mark; we 
therefore read the first figure as 2 and the second one as 9. 
The third dial marked 
100 shows the pointer 
just at the figure 9, but 
we do not know whether 
it has already reached 9 
or it is still 8; we look 
at the last dial to the 
right and see the point¬ 
er at I, showing that 
the third figure has al¬ 
ready gone beyond 9, 
and the last two figures 
are 9 and 1, the number 
of kilowatt-hours being 
2,991, provided there is 
no multiplier to be used with this meter. In this manner by 
watching the dial next to the right of the one which is 

203 






























HARPER’S EVERY-DAY ELECTRICITY 


being read it is easy to make sure of each figure in succession 
from left to right. 

The voltmeter and ammeter are connected to the line as 
shown in Fig. io. 

The wattmeter is connected to the circuit as shown in 

Fig. ii. 

Other electrical instruments are of no interest to the 
amateur. 


Chapter XIX 


TRANSFORMING ELECTRICAL ENERGY INTO MECHANICAL 

ENERGY 

E lectrical energy can be changed to mechanical 
energy. This transformation is brought about through 
the medium of an electric motor. 

The mechanical energy of a steam-engine is changed into 
electrical energy by the generator, or dynamo. This 
energy is sent out over the wire circuit. It may be changed 
back again into mechanical energy at any point and with 
trifling loss by the use of an electric motor. 

There is no mystery about the electric motor. It is 
merely a reversal of the process by which a generator 
produces current. In fact, a generator may be used as a motor 
by simply connecting it to an electric circuit. The power of 
the electric motor is the product of th e force exerted between 
a magnetic field and a conductor carrying an electric 
current. 

Look at an ordinary electric motor. You will observe that 
there are no sliding-pistons, no buckets, no belts, no gears, 
nothing to indicate where the mysterious power comes 
from. The motor consists of two essential parts—the frame 
and coils which combine to form the magnetic field and 
the rotating part, or armature, carrying the copper con¬ 
ductors. There is nothing to indicate whence comes this 
energy which turns the armature between the poles of the 
field-magnets. 

205 


HARPER’S EVERY-DAY ELECTRICITY 


The armature does not touch the pole-pieces of the field- 
coils, and yet it spins at high speed. Apparently no moving 
force is acting on the armature, and still it will produce 
enormous power. The motion of a small armature in a one- 
kilowatt (i-J^ horse-power) motor is so easy, so smooth, so 
noiseless that any one not familiar with its power would 
think it could be stopped with the pressure of a finger. 
Don’t try it! Invisible this force may be, and hard to com¬ 
prehend, but it is not to be denied. 

Let us try a few experiments and see if we cannot discover 
this source of power. 

We know from previous experiment that every magnet is 
quite surrounded with invisible rays called lines of force. 
These rays seem to pour out of the north pole and flow 
through the surrounding air to enter the south pole (Fig. i). 

This is equally true of every wire carrying an electric 
current. A magnetic field is set up about the wire. Inas¬ 
much as there are no north and south poles to such a wire 
the lines of force are distributed about the wire in circles, 
moving from left to right (Fig. 2). 

Remember that lines of force are constantly flowing 
between the magnetic poles in the field of the motor and 
another set of lines of force is flowing around the wires 
of the conductor in the armature of the motor (Fig. 3). 

The action of these opposing forces tends to push the 
armature wire down between the poles of the magnet when 
held in one position and up when held in another. 

Take a copper wire which is connected to a good battery 
and move it between the poles of a powerful horseshoe- 
magnet (Fig. 4). 

When the copper wire A, which is carrying a flow of cur¬ 
rent from the battery, is moved between the poles of the 
magnet without touching them an invisible force will seize 

206 


TRANSFORMING ENERGY 


upon the wire and tend to move it from the magnetic field. 
The force which moves this wire depends upon the strength 
of the magnet and the amount of curre 7 it flowing through the wire. 
If a very powerful electromagnet is used and a heavy current 
sent through the wire you will be surprised at the force 
exerted. 

The energy of an electric motor is secured by placing many 
such armature wires, carrying heavy currents, between the 
opposing poles of strong electromagnets. 

The force which moves the wire in the experiment de¬ 
scribed above is utilized in the motor to rotate the armature. 



The wires of the armature are arranged in the form of loops. 
With this arrangement the current flows in opposite direc¬ 
tions when the wires are near opposing poles. So, as you 
see, the magnetic force which is pulling one side of the loop 
down is pushing the other side up (big. 5)* 

207 





































HARPER’S EVERY-DAY ELECTRICITY 


When the lines of force are pushing up the left side of 
the loop before the north pole the same force is pushing down 
on the right side of the loop before the south pole. When 
the armature loop is pushed out of the way another imme¬ 
diately takes its place. In this way, and by using several 
poles, the motion of the armature is made continuous. 

Direct-Current Motors 

There are two kinds of electric motors—direct-current and 
alternating-current. Only direct-current motors can be 
used on direct lines. By this same rule only alternating- 
current motors can be used on alternating-current lines. 

Direct-current motors are subdivided into three classes— 
viz., series, shunt, and compound motors. Their class is de¬ 
termined by the manner of connecting the field and armature 
windings. Each class has its peculiar field where it is best 
suited for the work in hand. 

The series motor has the armature and field windings 
connected in series (Fig. 6). 

The series motor is best adapted for intermittent service 
where heavy loads must be brought to full speed without an 
excessive demand for energy. They are generally used for 
elevators, hoists, street-cars, electric railroads, etc. 

When unloaded, a series motor will race and continue to 
increase in speed until the armature is destroyed by the 
great centrifugal force set up. When a heavy load is 
thrown on the series motor the speed of the motor decreases, 
resulting in large currents through both armature and field, 
resulting in stronger pull to take care of the increased load; 
on the other hand, when a heavy load is thrown on the shunt 
motor the speed remains about as before, and the motor 
has to get its increased pulling-powers from increased current 

208 


TRANSFORMING ENERGY 


in the armature only. I he shunt motor cannot slow down 
like the series motor and take the increased load at a slower 
rate, but must tackle the job at about the same speed it 
maintains on a light load. In order to take care of the same 
loadings, therefore, the shunt motor would have to be much 
larger than the series motor. In short, when a fairly con¬ 
stant speed is desired a shunt motor can be used, but 



care must be taken to get one large enough to handle the 
heaviest load. When speed is not an important factor, but 
strong “pull” is required, the series motor is the one to use. 

The shunt motor has the armature and field-windings 
connected in parallel (Fig. 7). 

This is a constant-speed machine, regardless of the load. 
The only way to regulate the speed of a shunt motor is to 
insert resistance in series with the armature, which decreases 
the speed, or to insert resistance in the field, which increases 
the speed. But placing resistance in the armature circuit 
is a waste of energy. Only a certain amount of resistance 
can be placed in series with the field without excessive sparking. 

14 209 


























HARPER’S EVERY-DAY ELECTRICITY 


The compound motor, as the name suggests, is a com¬ 
bination of the series and shunt type (Fig. 8). 

This machine has two distinct field-windings, one in 
series with the armature and one in parallel with it. 1 he 
speed of this motor depends upon the relative value of the 
shunt and series windings. 

Alternating-Current Motors 

The alternating-current motors are divided into three gen¬ 
eral classes—the induction-motor , the synchronous motor , and 
the commutator-motor . The induction-motor is practically 
a constant-speed machine. The rotor may be either short- 
circuited or wound. In motors of the wound type the speed 
may be increased by inserting resistance in the rotor circuit. 
The squirrel-cage type of induction-motor is very simple. 
It is compact and reliable wherever a constant speed is 
wanted. It will start under full load. If started with a 
light load an automatic starter, or compensator , is used to 
keep the current within the safety limit. In the wound 
type of induction-motor slip-rings are provided so resistance 
may be inserted in the rotor circuit to vary the speed. 

The synchronous motor will not start under load. It 
must run at one speed. The field is excited by an in¬ 
dependent source using direct current. They are seldom 
used except where constant speed is necessary and a large 
amount of power required. 

In the synchronous motor the electrical energy is im¬ 
pressed upon the armature, fed directly to it from the line, 
and the fields excited from a separate direct-current source. 
In the induction-motor the electrical energy from the line 
is impressed on the field, the current in the armature being 
induced by transformer action. The induction-motor is 


210 


TRANSFORMING ENERGY 


essentially a constant-speed machine. Its speed can be 
varied by varying the number of poles in the field. 

1 he synchronous type of motor is not in common use. 
It is seldom employed where the induction-motor can be 
used, but it has marked advantages over the induction- 
motor in some cases. It could be used advantageously in 
place of an induction-motor where the latter would seriously 
interfere with the voltage regulation of the line. It re¬ 
quires more care than an induction-motor, is not self¬ 
exciting, and is not easily started. Single-phase synchro¬ 
nous motors cannot start themselves at all; they must have 
an auxiliary starting-device. Two and three phase syn¬ 
chronous motors will start themselves if they are free of 

*/ 

load. After they attain normal speed they can be loaded 
to capacity. 

The commutator-motor is a later invention. It has the 
advantage of permitting a wide range of speed by varying 
the voltage. 

There are three different classes of the above-mentioned 
alternating-current motors— single-phase , two-phase , and 
three-phase. Each class has its own peculiar character¬ 
istics and uses. 

Devices are made so a single-phase motor can be used 
on a two or three phase line, or vice versa. 

The dissembled view of a five-horse-power induction- 
motor will enable any one to understand its construction 

(Fig. 9). 

Power Applications in the Home 

The burden of housework has been materially lightened 
by electricity. Small motors are now made purposely to 
drive the washing-machine and the wringer, to operate the 

211 


HARPER’S EVERY-DAY ELECTRICITY 



Fig. 9 


DISSEMBLED VIEW OF A FIVE-HORSE-POWER INDUCTION-MOTOR 

vacuum cleaner, to sharpen knives, grind the foodstuffs, 
freeze the ice-cream, and to do all the other hard work about 
the house. These motors are very easily installed. Nearly 
all of them can be connected to the lighting circuit with an 
ordinary screw-plug and flexible cord which is readily 
attached to the electric-light socket in place of the lamp. 

Electric Fans 

Electric fans are made in many sizes and styles, including 
desk-fans, ceiling-fans, oscillating-fans, wall-fans, etc. The 
ordinary portable eight, ten, and twelve inch fans are best 
suitable for the home. They cost but a few dollars each. 
The eight-inch fan (its size determined by the diameter of 
the fan) is light and easily carried from room to room. It 
consumes even less current than a small electric lamp and 
may be operated all day long for four or five cents. The 
ten and twelve inch fans take but little more current, 

213 



TRANSFORMING ENERGY 




The electric fan is nothing more or less than an ordinary 
metal propeller fan of four or six curved blades, affixed 
directly to the armature, or rotor, of the tiny motor. The 
whole is mounted on a suitable base and standard. The 
revolving blades are protected by a wire guard or screen. 
The whirling blades catch the air and propel it out in a 
strong current. These fans are also made to oscillate, to 
swing back and forth, if desired. 

Fans are made for both direct and alternating current and 
for anv standard voltage. Care should he taken when buying 


fans to know the kind of current and the voltage. Only iio- 
volt fans should be operated on no-volt circuits, and so on. 

213 


DIRECT-CURRENT MOTORS 


DISSEMBLED VIEW OF DIRECT-CURRENT MOTOR 














HARPER’S EVERY-DAY ELECTRICITY 


Direct-current fans will not run on alternating-current 
lines, and vice versa. 

The Kitchen Motor 



A small motor can be arranged in the kitchen to do much 
of the hard work in connection with the preparation of food. 
This motor is easily connected to the ice - cream freezer, 

the coffee-grind¬ 
er, butter-churn, 
dough - mixer, 
fruit-press, pota¬ 
to-peeler, meat 
and food chopper, 
washing-machine, 
wringer, and ven¬ 
tilator, and for any 
other applications 
where power is re¬ 
quired. 

A small one- 
sixth to one-quar¬ 
ter horse - power 
motor is amply 
large enough for 
the kitchen. These motors can be operated from the lamp- 
socket. They consume about 300 watts of electricity. Each 
motor is provided with a slotted base so it can be bolted to 
the floor, walls, or ceilings. The kitchen devices can be op¬ 
erated by a system of shafting and suitable pulleys (Fig. 10). 

The proper speed for each device is determined by the 
size of the pulleys used. The method of figuring pulley- 
speeds is described in a previous chapter. 

A small motor is excellent for driving the small tools of 

214 


ALTERNATING-CURRENT INDUCTION-MOTOR 



MOTOR-DRIVEN WASHING-MACHINE AND WRINGER 



















































HARPER’S EVERY-DAY ELECTRICITY 


the boy’s work-shop, such as the lathe, saw, and boring- 
mill. It can also be connected to the grindstone, ash- 
sifter, cream-separator, and any other small power device. 

A small electric motor is almost a necessity on the country 
place or farm where electric current is available. Every 

day the electric 
wires are reach¬ 
ing farther and 
farther into the 
country. More 
and more country 
people are install¬ 
ing electricity for 
light and power. 

The first cost 
of a one - horse¬ 
power motor is 
about fifty dol¬ 
lars; the average operating cost of the motor will be 
about six cents per horse-power-hour. 

Installing Electric Power 

In installing electric motors care must be taken to see 
that they are properly fused. Any motor will work itself to 
death, so to speak. It will struggle with any load until i' 
actually burns itself up. Suitable fuses should be placed 
between the motor and the line to protect it in case of over¬ 
load. Circuit-breakers, which automatically open the line 
when too much current tries to pass, are used for this pur¬ 
pose with large motors. The circuit-breaker is a spring- 
switch operated by an electromagnet. An excessive current 
operates a trigger, and the spring throws the switch open. 

216 






























TRANSFORMING ENERGY 


Electric motors are the most convenient form of power. 
They can be had in all sizes, from a mere fraction of a 
horse-power to single units of 6,000 horse-power. They 
are free from noise, dirt, and danger, and are adaptable to 
all forms of work. Electric power is gradually superseding 
all other forms in mills, factories, machine-shops, etc. As 
the electric motor can be connected to the machine itself, it 
eliminates all power loss through long shafts, pulleys, and 
flapping belts. 

When buying a motor you must know whether it is to be 
used on direct or alternating current and the electrical 
pressure of the line, or voltage. 

If your place is supplied with alternating current, buy 
an alternating-current motor only, and be sure to specify 
whether it is single or polyphase current and the number 
of cycles. 

Alternating-current induction-motors can be safely used 
in the house or barn without fear of fire, as they will not 
spark. Direct-current motors for farm service should be 
installed in a separate fireproof building or inclosed with a 
protective cover. 




Chapter XX 


HELPS FOR THE SMALL MOTOR-BUILDER 

T HE first electric motor should be but a toy. Never 
attempt to construct a motor of any size until you 
have fully mastered the construction details of a little one. 

Toy motors are not hard to make. If one has a fully 
equipped work-room with a small lathe the task is very 
simple. Lathes and work-shops are not absolutely neces¬ 
sary. A very good motor can be built with very few tools 
on a corner of the kitchen table. 

Not every boy has a good metal lathe, with the proper 
tools for turning and finishing iron. Excellent work can be 
done with a wood-turning lathe for small work by using 
soft-iron parts and turning them down with a file. Center 
the work in the lathe, turn rapidly, and hold the file against 
the part to be cut away. In the absence of a lathe the iron 
parts of the motor can be built up out of sheet-iron strips. 

By following the instruction given below, illustrated in 
detail with drawings, a toy motor can be easily constructed. 

For the sake of simplicity let us combine the motor frame 
and the electromagnet into one piece. It would be a very 
difficult job to make this frame of a single piece of iron 
unless a pattern was made first and a casting poured. But 
we can make even a better frame by building it up out of 
sections, or laminations, cut from sheet iron. Sheet iron 
is soft and can be readily cut with a pair of tinsmith’s shears 

218 



HELPS FOR THE MOTOR-BUILDER 


or a fine metal saw. If it bends it can be readily straight¬ 
ened with a block and mallet. The rough edges left by the 
shears or saw can be easily worked down smooth with a 
file. First make a good pattern out of heavy cardboard to 
the dimensions given in Fig. i. 

Lay this pattern on a piece of sheet iron and cut out a 
duplicate. Work carefully and cut true to the pattern. 
When the section is cut in the rough finish it down smooth 
and nice with a file. Use a round file on the pole-pieces and 
see that they are circular and true. 

When the first section is done cut out enough more strips 
to build up a frame for the motor one inch thick. If the 
sections are straightened out with a mallet and block it is 
not necessary to bolt them together. One of the sections, 
the middle one, should be left with a notched spur on 
either side so the frame can be fastened to the base when 
completed (Fig. 2). 

The sections of sheet iron are stacked together and bound 
firmly in place by wrapping with insulation tape or cloth 
dipped in shellac varnish. Wind this firmly about the 
“necks”; cut away for the electromagnet - coils. The 
electromagnet is wound with five layers of well-insulated 
fine copper wire. Lay on five layers to each coil. Be sure 
to have an equal number of layers, and see that the wire 
is wound the same way in both instances. Fig. 3 shows the 
frame with one coil wound and the other side with the 
insulation ready to receive the second coil. The ends of the 
copper wire are brought out behind the frame and fastened 
to terminals for connection with the battery cells. 

Making the Armature 

Nearly every one has difficulty making the first armature. 
This is usually the result of too much haste. In the hurry 

219 


HARPER’S EVERY-DAY ELECTRICITY 


to get the motor done—for youth is often as impatient as 
enthusiastic—the important little details of the armature 
are slighted, and consequently the motor will not run. 




Build up the armature out of sheet-iron disks much the 
same way as the frame was constructed. The diameter of 
the frame inside the pole-pieces is one inch. Therefore 
the armature must be a trifle less so it can revolve between 
the poles without quite touching. Cut out a disk of card¬ 
board as shown in Fig. 4. 

The disk should be fifteen-sixteenths of an inch in di¬ 
ameter. This will leave the thickness of a sheet of paper 

220 


























































HELPS FOR THE MOTOR-BUILDER 


between the finished armature and the pole-pieces. Mark 
the disk into six equal sections, as shown above, where it is 
to be cut for the insertion of the armature coils. When the 
cardboard disk is done, cut out as many sheet-iron disks as 
there are sections in the frame, or so the armature will be 
equally as thick as the frame. Drill a hole for the armature 
shaft exactly in the center of each section. With a small 
file cut the slots for the coils. Be exact about this cutting. 
They must be true to the pattern. 


Mounting the Armature 


The armature is mounted on a rod or spindle. Thread 
the spindle at each end so the armature sections can be 
fastened in place with lock-nuts as shown in Fig. 5. 

It is easy enough to mount this armature in a wooden 
frame so it can be whirled between the poles of the electro¬ 
magnet without touching. If it should touch any little 




Fig. 8 F'g- 7 


irregularity can be corrected with the use of a sharp file. 
Do not forget that files get dull from service the same as any 

221 













































HARPER’S EVERY-DAY ELECTRICITY 


other tool. It is not practical to sharpen files. Old ones 
are thrown away. 

Making and mounting the commutator for this motor 
requires more skill than making any other part. The best 
and easiest way is to make a small wooden ring which can 
be slipped over the armature shaft. This ring may also be 
turned from hard rubber, lava-board, or any other good 
insulating-material which can be readily worked. Over this 
ring mount a thin brass sleeve. Tack the brass to the wood 
in six places as shown in Fig. 6. 

If small tacks are hard to get make them out of pins with 
a file. When the tacks are all in place cut the brass ring 
into six sections as shown in Fig. 7 and fill the cuts with 
sea ling -wax. 

The armature is wound with six loops of insulated copper 
wire. One end of the wire is fastened to a section of the 
commutator, either through a small hole or by solder¬ 
ing. The wire is wound once around the armature and 
fastened to the opposite section of the commutator 
(Fig. 8). 

When all six of these coils have been laid in place the 
armature is ready to be mounted in the frame so it can be 
whirled between the pole-pieces of the electromagnet. 
The armature shaft can be set up in a small wooden frame. 
First the screw-threads should be filled with solder and 
smoothed off with a file. Sealing-wax can be used for this 
purpose, but it will not last so long as solder. The com¬ 
mutator brushes are merely two strips of brass arranged to 
press lightly against opposite sides of the commutator 

(Fig- 9)- 

This type of motor is connected so the armature and 
the field are in series. Two or three ordinary dry-battery 
cells ought to make it run very nicely. 

222 


HELPS FOR THE MOTOR-BUILDER 


A Larger Motor 

1 he design for larger motors varies considerably. 

In order to assist those who are interested in motor- 
building the following plans and specifications have been 
prepared for a motor large enough to operate a small fan 



or to drive the toy machinery such as almost any boy 
possesses. 

The frame of this motor is also built up of sheet-iron 
sections because they are easier to make in this way. Cut 
out, as before, a cardboard pattern to the dimensions 
given in Fig. io. 

The pattern cannot be made perfectly true without using 
a square and compass. Work carefully and be sure that the 
pattern is laid out exact before cutting the cardboard with 
a sharp knife. When the pattern is done, lay it on the sheet 
iron and cut out a duplicate. The sheet iron can be cut 
best with a hack-saw. This is a fine ribbon saw fastened in 

223 

























HARPER’S EVERY-DAY ELECTRICITY 


a suitable handle and made purposely for cutting iron. It 
will saw soft iron, such as sheet iron, almost as fast as a 
common saw will cut hard wood. By using a fine saw even 
the pole-pieces can be cut out, but they must be finished 
with a round file. It is best to lay the cardboard on the iron 
and mark the pattern out carefully with a scratch-awl, 
running the awl around the edge of the pattern. 1 he fol¬ 
lowing sections can be cut very easily by fastening the first 
finished section and the next strip in a good vise and sawing 
out the iron with the hack-saw. 

Saw out and finish enough sections to build up a pile one 
inch thick. The two sections which form the outside of 
this frame should be cut with “lugs,” which can be turned 
up with a pair of pliers. They are drilled for the bolts 
which fasten the finished frame to the wooden base of the 
motor. 

Mark each section of the frame for the binding-bolts, and 
drill four holes in each piece. Unless you can be exact with 
this work it is better to stack the sections, fasten them 
firmly together so they will not “creep,” and drill the four 
holes through the entire pile. Otherwise the holes may not 
jibe when finished. Insert bolts and fasten sections in place. 

Wind the electromagnet (the center connecting “neck” 
of the frame) with No. 18 gage cotton-covered copper 
wire, first covering that portion of the frame with cloth 
soaked in shellac varnish. When the first layer is on, 
cover with cardboard and varnish before starting the next 
layer. The finished coil should be about half an inch deep. 
Th is will require eight or ten layers. Be sure to leave long 
ends for making proper connections with the circuit. 

When a battery current is sent through this coil the frame 
will be strongly magnetic. Test it to see if it is all right in 
this respect before continuing. 

224 


HELPS FOR THE MOTOR-BUILDER 


Another Type of Armature 

A motor armature is a wonderful bit of mechanism. It 
assumes a hundred different shapes and forms as one pro¬ 
gresses in motor construction, from a single loop of copper 
wire to an intricate winding difficult to understand. 

For a motor of the size given above, standing nearly eight 
inches high, calling for an armature nearly three inches in 
diameter and an inch thick, a different type must be used. 

The armature for this motor is built of strips of sheet iron, 
or laminations , laid one upon another into a pile an inch 
thick. These armature laminations must be made with 
care, by the same process and tools as used in making the 
laminations for the frame. Make a good cardboard pattern 
as shown in Fig. n. 

It is easy enough to make this armature and to mount it 
upon a metal shaft, but winding it is quite another thing. 
Before any attempt is made to wind it a three-section com¬ 
mutator must be made and affixed to the shaft. A ring, or 
sleeve, of insulating-material is affixed to the armature shaft 
as in all motors of this kind. Cut three pieces of thin brass 
with an “ear,” or lug, as shown in Fig. 12. 

Tack these sections on the insulated part of the com¬ 
mutator so the lugs are toward the armature laminations. 
Be sure that the spacing between the three sections of this 
commutator occupies exactly the position in relation to the 
armature laminations as shown in Fig. 13. 

The armature is now ready to wind. Secure a small 
quantity of No. 22 cotton-covered copper wire. Cover the 
armature legs with a coating of paper and shellac and dry 
thoroughly. Now wind on four layers of the wire on each 
leg, or pole. Insulate each layer from the next with paper 
and varnish. Begin to wind from the bottom of the leg 

225 




15 


HARPER’S EVERY-DAY ELECTRICITY* 



nearest the shaft, leaving three inches of end so the wires 
can be connected to the commutator later. Wind all three 
coils in the same manner and in the same direction. The 
outside end of the first coil is now connected to the inside 
end of the next coil. All three coils are connected together 
in this way and fastened to the ears of the commutator as 
shown in Fig. 14. 

Study the drawings carefully. Be sure the armature- 
windings are put on and connected as shown. Be doubly 
certain that the commutator sections are arranged per 
diagram. 

Assembling the Motor 

Set the frame up on a polished hard-wood base an inch and 
a half thick and somewhat larger than the entire motor to 

226 











HELPS FOR THE MOTOR-BUILDER 


give it stability. Screw the frame firmly to this base at the 
four corners. The screws pass through the lugs on the end 
laminations of the frame heretofore described and left for 
this very purpose. 

A frame is necessary to support the armature between 
the pole-pieces. This frame can be built up of wood on 
either side of the motor or can be made of ordinary strips 
of one-eighth-inch brass bolted to the motor frame. The 
brushes, which send the current through the armature coils, 
are merely strips of spring-brass mounted on an insulated 
base and provided with binding-posts for convenience in 
connecting up the motor. 

When the motor is assembled connect the armature and 
field-winding in series with three or four ordinary dry cells. 
The motor can be reversed at will by installing a small 
reversing-switch on the base. The speed can be varied by 
placing a little resistance in the armature circuit. By 
mounting a pulley on the armature shaft this motor will 
develop considerable power for its size. 

Generators Can be Used as Motors 

As noted elsewhere, generators can be used as motors by 
sending a current of electricity through them. Therefore 
the small generators described in the chapter devoted to that 
subject can be used as small motors. 

It may well be that some who read these pages will aspire 
to make a small one-eighth to one-quarter horse-power 
motor for operation on the regular household circuit. In¬ 
asmuch as these circuits vary so widely, being all the way 
from low-voltage direct current to single, two, and three 
phase alternating current of no to 250 volts, no attempt will 
be made to describe such a motor. Those who have the 

227 


HARPER’S EVERY-DAY ELECTRICITY 


time and the tools, and who have progressed in the subject 
far enough to be capable of the work, must first determine 
exactly the kind of current available before they attempt 
such a motor. For instance, a one-quarter-horse-power 
motor suitable for low-voltage (20-volt) direct current cannot 
be used on uo-volt polyphase alternating current. For the 
latter a specially designed machine is necessary. Neither 
can a no-volt alternating-current motor be operated on a 
250-volt circuit. 


Chapter XXI 


THE INDUCTION-COIL AND THE OPERATION OF THE 

TRANSFORMER 

T HE study of induced currents leads afar into the won¬ 
derland of electricity. 

A piece of iron held near a magnet becomes magnetic. 
This is due to induction. The qualities of the magnet are 
transferred through the air to the iron. 

A piece of iron wrapped with an insulated wire through 
which a current of electricity is flowing also becomes a 
powerful magnet. This magnetism is also induced in the 
iron by the process known as induction. 

Induction means to lead in from one to the other. The 
current of the insulated wire, so to speak, is led in to the iron 
core and it becomes magnetic. 

Move a copper wire between the poles of a magnet, and a 
current will be induced or led into the wire. 

Induced currents are always the result of the cutting of 
lines of force. The amount of electromotive force induced 
depends upon the following factors: 

The speed of the conductor moving across the lines of 
force. The more rapid this movement the greater the 
E. M. F. induced. 

The strength of the magnetic field, or the number of lines 
of force. The stronger the field the greater the E. M. F. 
induced. 


229 


HARPER’S EVERY-DAY ELECTRICITY 


The number of conductors cutting the lines of force. The 
more conductors the more E. M. F. induced. 

The induced electromotive force depends upon the number 
of lines of force cut per second. 

Suppose a moving conductor cuts 100,000,000 lines of 
force each second and this induces, or creates, an E. M. F. 
of one volt. Then if it cuts 200,000,000 lines a second it 
will create a pressure equal to two volts. And so, to induce 
an E. M. F. of no volts the conductor would have to cut 
11,000,000,000 lines each second. 

By multiplying the number of poles in the magnetic field 
and thus increasing the number of lines of force; by mul¬ 
tiplying the number of conductors cutting these lines and 
increasing their speed per second the induced E. M. F. may 
be increased. 

It matters little whether we move conductors across lines 
of force or lines of force across conductors, the result is much 
the same. Out of this natural law of electricity grew the 
dynamo, or generator, as we know it to-day. And as a result 
of further research and investigation we have the induction- 
coil and the modern transformer. 

Let us follow humbly in the footsteps of the great Faraday 
himself in order that we may fully understand this process 
called induction. 

Faraday wound two insulated wires on a stick, being care¬ 
ful that they did not touch each other at any point. One 
of these wires was connected to a battery. The other was 
connected to a current-detector, or galvanometer (Fig. 1). 

Faraday noticed that whenever the current in the wire 
(No. 1) was made or broken a current was induced, or 
caused to flow, through the wire (No. 2), although this 
second wire was not touching the first wire. This was a 
wonderful discovery for that day and age. But Faraday 

230 


THE INDUCTION-COIL 


pursued the investigation still further. He noted that when 
the current was flowing steadily through the first wire no 
current was induced in the second wire. The current ap¬ 
peared only when the battery current was made or broken in the 
first wire. This induced current in the second wire flowed 
one way through the wire when the current was “made” 
and the other way when it was “broken.” 

Faraday next took an iron ring and wound half of it with 
coils, or turns, of insulated wire and connected this wire to a 
battery. The second half of the ring he wound with a 
second insulated wire and connected this to a galvanometer, 
or detector (Fig. 2). 

Now, the coils were not even close to each other, although 
wound upon the same soft-iron ring, or core. Strangely 



TZZZZZZZA 


S-IVT/ No.z 




No .Z 


Galvanometer 

Fig. 1 


Fig. 3 




/Cloth Sr Varnish. 

—_- /Cloth 



C fo s sSec 1 1 o rx 

Fig. 4 


enough, when a current of electricity was sent through the 
first coil it induced a similar flow of current in the second 
wire. This current, like that of the first experiment, was 

231 















































HARPER’S EVERY-DAY ELECTRICITY 

induced only on the “make’’ and “break” ot the battery 
current. 

The wire connected to the battery, or source of current, 
became known as the primary wire. The wire in which the 
current is induced was named the secondary wire, and so 
they are called to this very day. 

The first practical development of this induced current 
was the induction-coil. Now, the induction-coil is nothing 
more or less than a transformer. Its action is exactly the 
same as described in the Faraday experiments above. The 
induction-coil does not produce a current of electricity. It 
only transforms it from a high to a low voltage or from a 
low to a high voltage. 

The induction-coil of whatever size consists of a soft-iron 
core , and a primary winding connected to a source of current, 
such as a battery. Over this is wound the secondary coil 
of very fine wire, which is connected to the external circuit. 
In order to insure a steady flow of induced current through 
the secondary coil (because the induction takes place only 
when the current is made or broken) a little spring device 
called a vibrator is used to make and break the primary 
current very rapidly. 

It is no trick at all to make an induction-coil. Take a 
rod of iron five inches long and three-eighths of an inch in 
diameter. A bundle of small soft-iron wires, such as stove¬ 
pipe wire, of the same length and thickness will be even 
better. At each end fit a wooden disk to make of the 
whole a spool, as shown in Fig. 3. 

Drill a small hole through the right-hand end-piece just 
above the iron core. Wrap the core with cardboard and 
varnish. Wind a layer of rather coarse cotton-insulated 
copper wire by drawing it through the hole in the disk. 
When the first layer is done cover with cardboard and var- 

232 


\ 


THE INDUCTION-COIL 


nish. Put on another layer, winding the coils close together. 
1 his should bring the wire back to the same end where it 
started. Drill another hole through the wooden end and 
bring this wire out. Leave long ends for connecting with 
the circuit. Cover with cardboard and varnish. This 
completes the winding of the primary coil (Fig. 4). 

The secondary coil is laid over this in much the same way. 
First cover the primary coil with cloth and varnish. Very 
fine silk-covered copper wire is used for the secondary 
winding. As before, a hole is drilled through the wooden 
disk, or end-piece, and a length of the wire left for connecting 
purposes. Wind the fine wire close and carefully. Take 
good care not to break it, as it is very delicate. Over each 
layer place a protective covering of writing-paper. Lay on 
eight or ten layers. Take the end of the wire out through 
the wooden disk on the opposite side from where it was 
started. Cover the hole with cardboard and varnish for 
protection (Fig. 5). 

Take the vibrator from an electric bell and arrange it so it 
will make and break the circuit as shown in Fig. 6. 

The vibrator is adjusted so it plays with a steady hum. 
This sends a pulsating current through the coils. If the 
terminals of the secondary coil are brought close together 
a brilliant spark will jump across the intervening air gap. 

The induction-coil is a plaything. It can be used for 
many interesting experiments with Geissler tubes, etc. It 
is used in telephone work and to raise the voltage of battery 
currents for ignition purposes in automobiles and gasolene- 
engines. 

The Transformer 

The induction-coil is used to raise the voltage of direct 


current. 


233 


HARPER’S EVERY-DAY ELECTRICITY 


As the vibrator is clumsy, inefficient, and has many other 
serious defects, it cannot be used for heavy currents. For 
this reason alternating current has come into general use, as 
its voltage can be readily raised or lowered with a trans¬ 
former. 

As alternating current is continually surging back and 
forth through the line, no vibrating device to make and 
break its flow is necessary to create induced currents. 



Fig. 5 








Prima-ry 

A 

_I 


Egg 

m 

\Secondary 

B 



Core C 




Fig. 7 


Therefore, the transformer has no moving parts. It con¬ 
sists of but two coils of insulated wire wrapped around an 
iron core. 

The action of the transformer is still a matter of theory. 
Take, for example, the elementary transformer shown in 
Fig. 7. 

An alternating current is sent through the primary coil A. 
This induces a second current, alternating in character, in 
the secondary coil B. Obviously this current must travel 
through, or be transmitted by, the iron core C. 

Theory has it that the magnetism of the iron core, pro- 

234 





















































THE INDUCTION-COIL 


duced by the turns of the primary cod A, varies according 
to the ever-changing values of the alternating current 
traveling through the turns of the primary coil. Every turn 
of the primary coil is encircled with lines of force when the 
current surges through them. When the current swings 
from right to left of these lines encircle the wire in one 
direction. As the current changes from left to right these 
lines of force circle the wire in the opposite direction. There¬ 
fore the magnetism, or lines of force, in the iron core are 
constantly changing as they pass through a regular cycle of 
values. 

The lines of force created in the iron core are cut by the 
many turns of the windings of the secondary coil. This 
induces an electromotive force in the secondary windings. 

The value of the E. M. F. induced in this secondary 
winding depends absolutely on the number of lines of force 
cut per second. If a hundred lines cutting ten turns pro¬ 
duces the same E. M. F. as ten lines cutting one hundred 
turns any pressure can be obtained by varying the number 
of times the secondary is wound around the iron core. This 
is best explained by the following case. 

A pressure of no volts is desired. A certain primary and 
core give a pressure of one volt with ten turns. To obtain 
the desired no volts the number of turns on the secondary 
must be increased no times, or brought up to a total of 
i,no turns. This will give the desired no volts. 

In this way the voltage of an ordinary 2,300-volt alter¬ 
nating-current generator is “stepped up” to 60,000 volts 
for transmission (Fig. 8). 

The above diagram shows the complete layout of a 
modern high-tension alternating-current system. The cur¬ 
rent is generated at 2,300 volts. After it leaves the generator 
it is transformed, or stepped up, to 60,000 volts for transmis- 

235 


HARPER’S EVERY-DAY ELECTRICITY 


sion to the place where it is to be used. Here the voltage is 
stepped down for service. A rotary converter changes the 
alternating current into direct current for use on the street- 
railway lines, etc. 

The transformer does not generate electricity. It merely 
raises or lowers its voltage, with some loss in heat, etc. 




A certain number of amperes of current, at a certain pressure, 
are sent into it. 1 hey emerge transformed in value. If a 
hundred ampeies at 2,200 volts are sent into the transformer 
they may emerge as 3.3 amperes at 60,000 volts, and so on as 
desired. And, strange to say, when the secondary circuit is 
open there is practically no flow of current through the 
primary coils. Any one would think, just to look at the 
diagram of a simple transformer, that the current would 
short-circuit through the primary coils and blow the fuses 
on the line. Nothing of the kind happens. When the 
secondary circuit is open a counter E. M. F. is generated in 

236 











































THE INDUCTION-COIL 


the transformer which opposes the flow of current through 
the primary coil. This back flozu of current effectively 
balances the primary current so that no more current flows 
through the transformer when the secondary circuit is open 
than just enough to magnetize the iron core. This opposi¬ 
tion to the flow is properly called reactance. 

When the secondary current is allowed to flow, by turning 
on lamp after lamp, this reactance disappears in proportion 
to the amount of current flowing through the secondary 
circuit, allowing a proportional increase of current in the 
primary. In this way the transformer is always nicely 
balanced. 

The Value of the Transformer 

The transformer, being a device to raise or lower the 
voltage, or pressure, of the alternating current, is especially 



SMALL TRANSFORMER 


valuable for long-distance transmission. For many years 
the millions of horse-power available from our great water- 

237 








HARPER’S EVERY-DAY ELECTRICITY 


falls had little commercial value because they could not be 
utilized in any manufacturing. They were too far removed 
from manufacturing and shipping points. Even if the 
energy of the falling water was turned into direct-current 
electricity, such as was used before the transformer was 
invented in 1885, nothing was gained. It required enormous 
quantities of costly copper to transmit low-voltage direct 
current over even short distances. 

A heavy current of electricity at low voltage requires a 
large copper conductor. The same amount of energy at 
high voltage can be sent over a small copper wire. This is 
just as true of water. To produce 100 horse-power from 
water falling one foot, or with little pressure, would require 
an enormous amount of water. To produce 100 horse¬ 
power from water falling 1,000 feet, or under high pressure, 
requires but a thin stream and very little water. 

By raising the pressure, or voltage, of the electrical 
energy to 150,000 volts it can be sent for hundreds of miles 
over a wire no larger than your finger. If this voltage was 
dropped to 15,000 it would require a wire one hundred times 
as large. With copper costing about fifteen cents a pound 
this is a material saving. 

In the cities where the service wires extend for miles 
beyond the power-house it is important to transmit the 
current at 2,200 volts and then step it down with small 
transformers to no volts for household use. Not only is 
there a saving in cost of line material, but the voltage drop 
and line losses are less at the higher voltage. 


i 


Chapter XXII 


SMALL TRANSFORMERS FOR HOUSEHOLD CIRCUITS 

V ERY often it would be most convenient if low-voltage 
current could be taken direct from the house circuit 
for ringing door-bells, lighting small lamps, or for various 
experiments. 

Low-voltage apparatus can be operated from no-volt, or 
ordinary household voltages, by inserting resistance in series 
with the apparatus. For instance, a io-volt motor can be 
operated on a 120-volt line by connecting a no-volt lamp 
in series with the motor. 

The amateur who desires to utilize the household circuit 
for experimental purposes will do well to make a good 
resistance-box, or rheostat. This device is very simple and 
permits of any degree of resistance desired. 

The resistance-box is not a transformer. It does not 
“step down” the high voltage to a lower voltage. It con¬ 
sumes, by resistance, a portion of the electrical pressure, or 
voltage. This portion may be varied at the will of the 
operator. Consequently the resistance-box is far from being 
as economical as a transformer for the same service. 


Making a Resistance-Box 

Take a long piece of iron wire about the size of the lead in 
a pencil. Wind it upon a three-eighth-inch round stick to 
form a coil fifteen inches long. Lay on the turns tight and 

239 


HARPER’S EVERY-DAY ELECTRICITY 


close together. When this is done remove the stick and 
stretch the coil to twenty inches. This will leave a small 
air gap between each turn of the wire. 

Mount this on a wooden base ten inches square and an 
inch thick. Mark a six-inch circle in the center of this 
board. With a half-inch gouge-chisel work a circular chan¬ 
nel in this baseboard half an inch deep. Line this channel 
and cover the baseboard with asbestos paper and press the 
wire coils firmly in place (Fig. i). 

One end of the wire is brought out to a binding-post for 
connection to the circuit. The other terminal is connected 



to the center arm and post as shown in the above illustration. 
When completed the brass strip can be swung with the aid 
of the insulated handle, or knob, to any position on the coil. 
As the brass contact is moved along on the coil the amount of 
resistance-wire in the path of the circuit is increased. As 
it is moved back the amount is diminished. With this simple 
instrument a wide range of resistance can be had in an instant. 


Details of Transformer Construction 

No transformer gives ioo per cent, efficiency. Some of the 
best come very near this, only about 2 per cent, of the cur- 

240 











































TRANSFORMERS FOR HOUSEHOLD CIRCUITS 


rent being lost. There is an established ratio between the 
voltages in the primary and secondary coils. This is also 
true of the amperage (Fig. 2). 

If there are 10 turns in the primary coil shown above 
and 100 turns in the secondary coil the voltage obtainable 
from the secondary should be 10 times that put into the 
primary. But the amperage of the secondary, remember, 
will be but one-tenth of that of the primary. On the other 
hand, the watts obtainable from the secondary will be the 
same as from the primary, since the wattage of the line is 
always the produce of the amperes times the voltage. One 
ampere at 100 volts will do the same amount of work as 
100 amperes at a pressure of one volt. 

If a current of 100 volts and 10 amperes is sent through 
the primary coil a current of 1,000 volts and one ampere 
can be taken from the secondary. And this secondary cur¬ 
rent would have the same amount of energy as the primary 
current, less a trifling loss in the operation of the transformer. 

In large transformers solid-iron cores are not used, due to 
excessive heating and eddy currents. The core is built up 
of laminations which are partially insulated from each 
other. This eliminates, or reduces, the eddy currents. 
The laminations of the core are arranged to run at right 
angles to the current, otherwise the effect would be as bad 
as though solid iron was used. 

Building Small Transformers 

A small transformer to step down the house current from 
no volts to 10 volts is not hard to make. In design it is 
much like an electromagnet. It consists of two coils and 
an iron yoke as shown in Fig. 3. 

The yoke is simply two bolts four inches long connected 

16 241 


HARPER’S EVERY-DAY ELECTRICITY 


together with soft-iron strips of equal dimensions, leaving 
a space of three inches between the bolts, as illustrated. 
Wooden disks are slipped on the bolts to form spools. The 
spool A is wound with 500 ohms of No. 36 wire. Referring 


<- 4 in. -> 



t 


8 
• N 


I 


Fig. 3 


Fig. 4 


to the wire table, we find that the resistance for one foot of 
No. 36 wire is .512 ohm. To obtain 500 ohms resistance we 
will have to wind on about 1,000 feet of the wire. Cover the 
iron bolt with varnished cloth or cardboard. Cover every 
layer of wire with a piece of heavy writing-paper. Be sure 
the paper comes flush up against the wooden ends of the 
spool so the layers of wire cannot possibly touch one another. 

The spool B is wound with No. 13 wire in the same manner 
as the first spool, with varnished cloth over the core and 
writing-paper between each layer of wire. The finished 
transformer can be mounted on a suitable base. The 
terminals of the primary coil A are connected to the line 
and the terminals of the secondary coil B to the apparatus 
to be operated. 

A Core-Type Step-Down Transformer 


Transformers are made in two types. In the core trans¬ 
former the coils are wound upon the soft-iron core. In the 

242 


















































TRANSFORMERS FOR HOUSEHOLD CIRCUITS 

shell-type transformer the core surrounds the coils. The 
core type is easiest to make. 

Build up out of sheet-iron laminations a core 1-*^ inches 
thick, 6 inches high, and 4 inches wide (Fig. 4). 

To saw out the center of each lamination holes are drilled 
to admit the hack-saw blade. The finished core is smoothed 
and touched up nicely with a sharp file. The corners should 
not be too sharp. 

Where the coils are to be placed cover with pieces of heavy 
cotton cloth saturated with shellac. Dry and wind on the 
primary coils. Be sure to wind both legs in the same direc¬ 
tion, just the same as you wind an electromagnet. The 
primary consists of No. 23 insulated wire, 400 turns to each 
leg, or 800 turns in all (Fig. 5). 

Wind the primary wire evenly in snug layers. Over each 
layer place a covering of heavy paper or cotton cloth. Un¬ 
less the wire is wound tight the finished coil will be loose and 
unsatisfactory. Be careful not to break the wire. If it 
breaks it must be carefully spliced and insulated. 

Cover the primary coils with three or four layers of heavy 
cotton cloth and shellac liberally. Be sure the ends are 
long enough for proper connection when the coils are done. 

The secondary coil is laid immediately over the primary 
coil. This secondary coil is made up of about 40 turns of 
No. 13 insulated copper wire to each leg, or about 80 turns 
in all (Fig. 6). 

The finished coils are wound with a good coating of 
heavy cotton cloth, fixed in place with shellac varnish or with 
friction-tape. 

Connecting the Coils 

Care must be taken in connecting up the coils, or the 
transformer will not work at all. Take the primary coils 

243 


HARPER’S EVERY-DAY ELECTRICITY 


first. If they are right they are wound both in the same 
direction. When the two coils are connected the current 
flowing over the wire should move in opposite directions 
around the two legs of the core (Fig. 7). 

The finished transformer should be mounted on a suitable 
base and arranged so the terminals of the primary windings 





Fig. 6 


To lioVoH Line* 


loVoltLi 




Frra't Leg 

Conneci L<ag\s 

Second. Leg 

-— To 720 Voli line 


Lnmary 

Conn.ectxox\3 


Fig. 7 


Firsi Leg 
1 Connect Legs 

-Second Leg 

ToiOvoU Lme 

Secondary 

Connections. 


can be connected to the no-volt line. The secondary 
terminals are brought out to binding-posts so they can be 
connected to the secondary line, consisting of the electric 
bell, miniature lamp, small motor, or other apparatus re¬ 
quiring a low-voltage alternating current of about 10 volts. 

The small transformer offers an unlimited field for the 

244 





















































































































TRANSFORMERS FOR HOUSEHOLD CIRCUITS 


experimenter. From the very elementary device, consisting 
of but a few turns of the primary wire and several turns for 
the secondary, there is hardly a limit to the experiments 
possible. When one has mastered the principles of the 
transformer it is easy enough to figure out a machine of 
any desired size and to build it on the work-bench. 


Chapter XXIII 


A SMALL ELECTRIC PLANT FOR THE COUNTRY HOME 

E LECTRIC light, electric motors, electric heating and 
cooking are for those only who have electricity at their 
disposal. Electricity is vastly different from coal and 
gasolene. You can go to the village and buy a ton of coal 
and haul it home. You can burn this coal under a steam- 
boiler and utilize its energy to drive the farm machinery, to 
heat the house, or to cook the food. You can buy a few gal¬ 
lons of gasolene and carry it in a can. This liquid fuel can 
be used also to drive engines, to run automobiles, even to 
cook the food if necessary. But you cannot drive to town 
and purchase a gallon of electricity! 

Coal and gasolene were made for us many thousands of 
years ago when Dame Nature stored up the energy of the 
sun and locked it securely in her bosom for the benefit of 
mankind. If she has any electricity stored up for us we 
have not found it to date. 

% Those who live away from the cities and villages, where 
electricity is produced by central power-stations and dis¬ 
tributed about these centers for the convenience of cus¬ 
tomers, must make their own electricity on the premises. 

Electricity is merely a transformation of energy. There¬ 
fore, to make electricity we must first have a source of 
energy. Energy is available on the farm in several forms. 
A few farms have suitable streams of water from which a few 
horse-power of energy can be produced. Others can use 

246 



ELECTRIC PLANT FOR THE COUNTRY HOME 

large windmills with considerable success. And, very 
fortunately, those who live in the hilly and mountainous 
districts, where a steady wind is seldom available, are the 
very ones who have water-power. On the other hand, the 
level prairie land where water is absent is a favorite place 
for the four winds, and there is seldom a day when the wind¬ 
mill is idle for twenty-four hours. 

For those farms where neither wind nor water is available, 
and these are far in the majority, there is the gasolene-engine, 
which is a very compact and economical source of power. 

Essentials of the Private Plant 

Whatever the source of power, be it wind or water or en¬ 
gine, the plant must consist of a suitable generator, a storage 


AUXILIARY STORAGE-BATTERY FOR USE WHEN PLANT IS NOT RUNNING 

2 47 





HARPER’S EVERY-DAY ELECTRICITY 


battery to supply current when the driving-power is not 
working, a system of wiring for the buildings, and a suitable 
switchboard for the control of the current. 

The generator can be purchased in any size desired. 
For very small plants they are usually bought to supply a 
certain number of lamps—ten lamps, twenty-five, fifty 
lamps, etc. For larger sizes they are rated in kilowatts, a 
one-kilowatt machine being equal to one and one-third 
horse-power. 

The storage battery is composed of individual cells, and it 
may be as large or as small as desired. The wiring for the 
buildings differs in no way from that described in previous 
chapters. 

There is no better form of artificial illumination than 
electricity. It is the most convenient, the safest, and the 
cheapest when everything is taken into consideration. 
With a small electric-light plant the entire country home 
can be lighted from cellar to garret, including all the dark 
closets. The lines can also be readily extended to the yards, 
barns, stables, hen-houses, etc. With suitable switches 
these lamps can be controlled from the house. In case of 
trouble or an unusual noise in the night the yards and barns 
can be instantly illuminated by throwing a master switch. 

By installing a private electric plant any one can have all 
the electrical conveniences of the city. 


Uses of Electricity in the Farm Home 


Lighting 

Electric fan 

Sewing-machine 

Electric iron 

Washing-machine 

Wringer 

Mangle 


Frying-pan 

Griddle-iron 

Broiler 

Soup-kettle 

Cereal-cooker 

Egg-boiler 

Egg-beater 

248 


Vegetable-peeler 

Plate-warmer 

Heating-pad 

Curling-iron 

Shaving-mug 

Cigar-lighter 

Sealing-wax heater 


ELECTRIC PLANT FOR THE COUNTRY HOME 


Refrigeration 
Vacuum cleaner 
Radiant toaster 
Tea-kettle 
Coffee-percolator 
Chafing-dish 
Baby milk-warmer 
Radiant grill 
Waffle-iron 
Hot plate 


Corn-popper 

Water-heater 

Stove 

Oven 

Electric range 

Fireless cooker 

Sausage-stuffer 

Meat-grinder 

Coffee-grinder 

Bread-mixer 


Pumps for water-supply 

Ice-crusher 

Ice-cream freezer 

Buffer and grinder 

Furnace-blower 

Foot-warmer 

Air-heater 

Luminous radiator 


Electric Light for the Farm-House 

On an average, artificial illumination is required not more 
than four hours a day in most farm-houses. Only two rooms 
in the house need to be illuminated for this long every day— 
the kitchen and the living-room. Bedrooms are lighted for 
short intervals only, and the cellar and woodshed lights are 
snapped on for only a few minutes at a time. For the whole 
house and for the barn an average of three hours per day for 
each lamp would seem to be ample, and five lamps will 
afford much more light than now suffices for all the purposes 
of the farmstead. If the householder can get rid of the idea 
that if he introduces electric light he must have clusters 
of flashing bulbs all over his premises, then the electric light 
would seem to be within reach at a comparatively small 
expense. 

Electric Motors for the Home 

Small motors have a great variety of uses. Recently 
a young man purchased a tiny motor to drive his turning- 
lathe. He soon had it fitted so that it would run a polishing 
and grinding wheel, sanding-wheels, and small circular saws. 
Then he bought a large pulley-wheel and operated the wash¬ 
ing-machine with the motor. At the beginning of the warm 
weather he equipped the ice-cream freezer to be driven in the 

249 


HARPER’S EVERY-DAY ELECTRICITY 



FOURTEEN-HORSE-POWER GASOLENE ELECTRIC SET, SHOWING SWITCHBOARD FOR 

CONTROL IN THE GARAGE POWER-HOUSE 


same way. There are many other purposes which this 
kind of motor could be made to serve in the city or the 
suburbs. 

The General Utility is a small motor designed especially 
for use in the home. It is provided with several attachments, 
any of which can be easily added or removed. With these 
the motor will run the sewing-machine, a polisher for cleaning 
silverware, a sharpener for tools and knives, fans for ventilat- 

250 











ELECTRIC PLANT FOR THE COUNTRY HOME 


ing the house or furnishing a draught for the furnace, a lathe, 
or any other similar device. By means of a flexible shaft 
it can be employed in polishing brass and other metal trim¬ 
mings on an automobile, carriage, or fixtures, since a handle 
makes it easily portable in one hand, while the other is free 
to apply the polisher. 

Electric fans are seldom classified as motors, but they are 
nothing more or less. 


SIZE OF MOTORS TO USE ON DIFFERENT HOUSEHOLD 

MACHINES 


MACHINE 

H.-P. OF MOTOR 

MIN. 

MAX. 

SIZE MOST 

COMMONLY" USED 

Sewing-machine. 



l/'iO 

Buffer and grinder. 

1/30 

1/30 

1/30 

Vacuum cleaner. 

1/8 

5 

1/8 to 1/4 

Ice-cream freezer. 

1/8 

i/4 

1/8 

Washing-machine. 

1/8 

2 

1/8 to 1/2 

Meat-grinder. 

1/4 

3/4 

i/4 

Water-pump. s . 

i/4 

1 

1/2 


Electric Motors for Farm Power 

It has been practically demonstrated that electricity is the 
ideal power for farm use, because it can be readily trans¬ 
mitted with safety and economy to any point where needed 
and applied in any quantity desired. With electricity the 
power-plant, whether the energy is generated from water, 
steam, or gasolene, is always located in one place and the 
current is transmitted over insulated wires to the milk- 
room, the dairy, the hay-loft, or to any other part of the farm 
and farm-buildings to do the work or to dispel the darkness. 

The amount of power required to operate most farm 

251 




















HARPER’S EVERY-DAY ELECTRICITY 


machinery is small. The presence of a plant of sufficient 
capacity to operate one or two particular machines often 
makes it possible to use the power for many of the other 
purposes. The amount of work that a small motor will do 
may be judged from the table on the following page. 



CREAM-SEPARATOR AND WASHING-MACHINE OPERATED BY ONE-QUARTER- 

HORSE-POWER MOTOR 

252 











ELECTRIC PLANT FOR THE COUNTRY HOME 


SIZE OF MOTORS TO USE ON THE DIFFERENT FARM 

MACHINES 


MACHINES 

H.-P. OF MOTOR 

MIN. 

MAX. 

SIZE MOST 

COMMONLY USED 

ON AVERAGE 

FARMS 

Feed-grinders (small). 

3 

IO 

s 

Feed-grinders (large). 

10 

30 

15 

Ensilage-cutters. 

10 

25 

15 to 20 

Shredders and huskers. 

10 

20 

15 

Threshers, 19-in. cylinder. 

12 

18 

15 

Threshers, 32-in. cylinder. 

30 

SO 

40 

Corn-shellers, single-hole. 

3/4 

I-I /2 

I 

Power-shellers. 

10 

IS 

15 

Fanning-mills. 



!/4 

Grain-graders. 



1/4 




Grain-elevators. 

1-1/2 

s 

3 

Concrete-mixers. 

2 

10 

5 

Groomer, vacuum cleaner. 

1 

3 

2 

Groomer, revolving-system. 

1 

2 

1 

Hay-hoists. 

3 

15 

S 

Root-cutters. 

1 

S 

2 

Cord-wood saws. 

3 

10 

5 

Wood-splitters. 

1 

4 

2 

Hay-balers.... '.. 

3 

10 

7-1/2 

Oat-crushers. 

2 

10 

S 

Water-pump. 

1/2 

5 

3 

Cream-separator. 

if 10 

i /4 

1/8 

Churn. 

1/8 

3 

i /4 

Milking-machine, vacuum-system 

1 

3 

3 

Refrigeration. 

1/2 

10 

S 


Righting Wrong Impressions 

A great many wrong impressions have resulted from the 
recently awakened interest in small electric plants for the 
country place. A man in Kansas purchased several electric 
lamps and was disappointed because they would not light. 
He was very much surprised when he found out that he 
could not use them without installing a private electric plant. 
Another farmer in the Northwest bought an electric motor 

253 








































HARPER’S EVERY-DAY ELECTRICITY 


and, of course, it was useless for him without a source of 
current to supply the motor with electricity. A motor 
without electricity is of no more use than a gasolene-engine 
without gasolene. 

It is well to know something about electricity before 
buying electrical apparatus of any kind. 

Remember that a small , low-voltage, private electric plant is 
suitable for electric lighting only. These small plants, driven 
by windmill or water-wheel, or even by a small engine, are 
usually of low voltage and produce only a small current. 
They are suitable for lighting purposes only. Small motors 
and heating-devices are not yet standardized in these low 
voltages and, therefore, are not readily available for such 
low-voltage lines and service. Perhaps some day in the 
near future electrical devices will be standardized for low- 
voltage lines, but that day has hardly arrived as yet. 

A low-voltage electric plant for lighting service only is the 
cheapest and easiest kind of plant to install. But, if small 
motors are to be used, if the current has to be transmitted for 
any distance, if standard heating and cooking devices are 
desired, then a plant of standard capacity, of no volts , 
should be installed. 

The reason why the higher-voltage plant costs somewhat 
more is found in the storage battery. Each storage-battery 
cell will give but 2.5 volts. Obviously it would require but 
10 cells to supply a 20-volt line. But it would take 55 cells 
to supply a no-volt line. If the cells cost about $5 each it 
is easy to see that the 55-cell battery will cost $275 against 
$50 for the 20-volt line. 

The Power of Water 

A great many farm streams are running to waste without 
lifting a finger, figuratively speaking, to assist with the farm 

254 


ELECTRIC PLANT FOR THE COUNTRY HOME 


work or to help keep down expenses. It is surprising what 
a small amount of falling water will produce one horse-power 
of energy. Even a small trout-brook can be made to light 
the premises and to supply power for the small chores about 
the farm. 

Falling water possesses more power than we suppose. 
Water acts as a moving power either by its weight—which is 
over sixty-two pounds to the cubic foot—or by its pressure 
or impact. The power of a fall of water is equal to the 
weight of its volume times the vertical height of its fall. 
To compute the power of falling water it is necessary to 
multiply the volume of flowing water in cubic feet per second 
by its weight —62-^2 pounds—and this product by the vertical 
height of the fall in feet, and divide by 550, which is the 
number of foot-pounds representing one horse-power for one 
second. 

A common level can be used to measure the fall of a 
stream (Fig. 1). 

By setting up the level and sighting over it to a suitable 
marker, or to an adjustable marker on a pole, the fall of any 



stream may be figured out with considerable accuracy. If 
strict accuracy is necessary a surveyor can ascertain the fall 
in a few hours’ work with a surveying-instrument. 

255 








HARPER’S EVERY-DAY ELECTRICITY 


To weir a small stream, or to find how many cubic feet of 
water are flowing per second, a temporary dam has to be 
built across the stream (Fig. 2). 

How to Make a Weir 

Place a notched board or plank in the stream at some 
point where a pond will form above it. The length of the 
notch in the plank should be from two to four times its 



Fig. 2 


WEIR 

depth where small quantities of water are to be measured 
and four to eight times the depth where large quantities 
are to be measured. The edges of the notch should be 
beveled, as shown in sketch, with the slant down-stream. 
The distance between the bottom of the notch and the level 
of the water in the pool below the dam should not be less 
than twice the depth of the notch. Drive a stake in the 

256 





ELECTRIC PLANT FOR THE COUNTRY HOME 


pond about six feet above the dam, with its top precisely 
level with the lower edge of the notch, then complete the 
dam so that all the water will flow through the notch. The 
depth of the water flowing through can easily be measured 
by means of a rule placed on top of the stake as shown in the 
sketch. It is essential in building a weir that the bottom 
of the notch should be as nearly level as possible. 

One side of the weir is made so it can be pulled back and 
forth to control the water falling over the face of the weir. 
This slide is adjusted until the falling water is just a foot 
deep. Then by simply multiplying this by the linear feet 
of the “apron,” or the width of the stream, will give the 
volume of water in cubic feet. If the apron is ten feet 
long and the water falling over it one foot deep, then the 
total volume is ten cubic feet. If the depth of the water 
is but six inches, then the total cubic feet will be five. 

The volume flowing over the weir per second is found by 
putting a suitable float in the stream and timing the speed 
of the stream. Set up two markers ten feet apart (Fig. 3). 



Fig. 3 


Time the passage of the float between the stakes. If it 
takes the float just one second to traverse this known dis¬ 
tance, then we can assume that the stream is flowing 10 x 10, 
or 100 cubic feet per second. 

Multiply the volume of flowing water in cubic feet per 
17 257 










HARPER’S EVERY-DAY ELECTRICITY 


minute by its weight, 62-J/2 pounds, and this product by 
the vertical height of the fall in feet, and divide by 33,000, 
the number of foot-pounds representing one horse-power for 
one minute. A stream of water when flowing over a weir 
five feet in width by one foot in depth at the rate of one foot 
a second and having a fall of twenty feet develops 11 horse¬ 
power. 

The Horse-Power of the Wind 

Where there is a strong prevailing wind a good windmill 
will give quite a little power. 

The following table shows the horse-power which can 
theoretically be realized from a 28-foot wheel exposed to 
winds of various velocities. 


SPEED OF WIND 

M. P. H. 

H.-P. 

SPEED OF WIND 

M. P. H. 

H.-P. 

2.25 

.04 

22.5 

40 

6.7 

I . I 

33-5 

135 

II .2 

5 

45 

520 

15-7 

13 

67 

1,080 


The power available should increase with the cube of wind 
velocity (since the energy of the air particles increases with 
the square of their velocity and the number of them striking 
the wheel-blades per second increases in direct proportion 
to the wind velocity). It is not practicable to construct a 
mill which will utilize with equal efficiency a light breeze 
and a strong wind, hence the curvature and setting of the 
blades should be such that the mill works most efficiently 
when exposed to a wind of the velocity generally prevailing 
in the district concerned. If a wheel be designed to utilize 
with maximum efficiency a wind of 22.5 miles per hour it 
will not run in a 7-miles-per-hour breeze, since the power 

258 











ELECTRIC PLANT FOR THE COUNTRY HOME 


corresponding to this wind is less than the power required to 
overcome the light-load losses of the wheel and its gearing. 
Breezes of 8 to 15 miles per hour are much more common 
than 20-miles-per-hour winds, hence it is generally advisable 
to employ, for driving electric generators, a very light wheel 
which will start work in a 3.5-miles-per-hour wind and which 
can still be used when the wind rises to 10 miles per hour. 
Such a wheel could not be exposed fully to a 30-miles-per- 
hour wind, and for safety a device should be mounted on 
the main wheel so that when the wind pressure exceeds a 
certain limit the inclination of the blades is changed against 
the control of a spring in such a manner as to reduce the 
effective area exposed to the wind. The control-springs 
may conveniently be set so that they come into operation 
when the wind velocity exceeds 16 miles per hour and so 
that the output of the mill is constant in winds above 
18 miles per hour. 

The Gasolene-Engine 

/ 

It is estimated that there are at least two million gasolene 
and oil engines on the farms in this country at the present 
day, and this number is being added to at the rate of 500,000 
annually. The average size of these engines is about seven 
horse-power. 

Any good gasolene-engine may be used to drive an 
electric generator, provided it gives a fairly constant speed. 
Of course, it will be necessary to obtain the correct speed 
ratio between the engine and the generator, but this is 
easily figured out. 


Chapter XXIV 


INSTALLING A SMALL ELECTRIC PLANT 

T HE simplest, cheapest, and smallest lighting-plant 
which it has ever been my good fortune to hear about 
consists of but a small battery composed of eight dry cells 
and two low-voltage battery lamps. With this simple out¬ 
fit and the necessary wiring and fixtures, costing less than 
three dollars all together, a barn and stable are lighted with 
electricity. 

This battery lighting outfit is very handy in the wagon- 
house and stable. It eliminates the striking of dangerous 
matches and the use of lanterns. As the lamps are used 
but a few minutes at a time, only long enough to unhitch 
and put the horse away, the batteries will last for months 

(Fig. i). 

This diagram shows the wagon-house and adjoining horse- 
stable lighted with two six-volt eight-candle-power lamps 
from a battery of eight dry cells. The cells are arranged in 
series-multiple, as shown in the picture, four cells in series. 
The battery is placed out of the way on a shelf in the wagon- 
house. The miniature bases for the lamps will cost ten cents 
each, and two small snap-switches will cost about the same. 
The two six-volt battery lamps of eight candle-power each 
will cost about thirty-five cents each. The amount of 
No. 18 wire necessary will depend, of course, on the distance 
the lamps are placed apart and removed from the battery 

260 


INSTALLING A SMALL ELECTRIC PLANT 


source. The wires are strung on proper insulators, and the 
switches are arranged on the side-walls near the door where 
they are most convenient upon entering and leaving the 
building. 


A Small Windmill-Plant 

What is perhaps the smallest windmill-driven electric¬ 
lighting plant is located in Wisconsin. This tiny plant 
supplies current for twenty - four lamps (although not 
all at the same time) and is operated entirely by the farm 
windmill at a total cost of a few cents a year for lubricat- 
ing-oil. 

The farm consists of about a hundred acres, and is devoted 
to stock-raising and dairying. The power - windmill is 
12 feet in diameter, with a vertical shaft extending down 
the tower; • attached to it are the power-pulleys, etc. In 
addition to driving the electric-light dynamo this mill is 
used to operate a drill-press, grindstone, corn-sheller, small 



Circuit- breaker 


Fig. 1 Fig. 2 

saw, washing-machine, grain-elevator, and feed-grinder. 
The dynamo is located in a small building at the base of the 
windmill tower. This dynamo has a capacity of six amperes 

261 





















































HARPER’S EVERY-DAY ELECTRICITY 


at 35 volts, or .21 kilowatt, when driven at full speed of 
450 revolutions a minute. The variations in speed, due to 
irregularities in the wind, are overcome by a small auto¬ 
matic switch placed in the circuit between the generator 
and the storage batteries which prevents any accidents to 
the apparatus by breaking the circuit when a certain range 
of speed has been passed. 

This tiny plant illuminates the home, yards, and the barn 
buildings. All the lamps receive their current from the 
storage battery, the charging of which is the dynamo’s only 
function. The entire plant, including windmill, generator, 
battery, wiring, lamps, etc., could be duplicated for not 
more than $250 (Fig. 2). 


Details of a Water-Power Plant 

A farmer in eastern New York has harnessed a small 
trout-stream to an electric generator. There was an ancient 
sawmill dam on this stream, so he did not have to go to the 
expense of making an entirely new dam. A few repairs were 
necessary, however. The volume of water is small, but the 
fall is 15 feet. He installed a nine-inch upright water-tur¬ 
bine in a wooden case which he built himself. This wheel 
develops about five horse-power. It is belted to a three- 
kilowatt, 125-volt, direct-current generator. He next in¬ 
stalled a suitable water-wheel governor to insure a steady 
flow of electricity. 

The plant is started and stopped with a 700-foot wire 
running to the home of a neighbor whose buildings are also 
lighted from this plant. 

This wire controls a valve and counterweight. The entire 
plant cost about $500, distributed as follows: 

262 


INSTALLING A SMALL ELECTRIC PLANT 


Dynamo, 3-kw. (second-hand). $ 50 

Water-wheel, 9-in. (naked). 55 

Governor (new). 75 

Wire (7,400 ft.). 210 

Labor (installing wheel). 40 

Fixtures, lamps, etc. 38 

Small motor (2 h.-p.). 50 


Total.#518 


The direct-current generator is of standard voltage and 
amply large enough to light the farm buildings and the home 
of a neighbor. It will supply current for electric heating and 
cooking devices and for motor power up to about four 
horse-power. This plant is not equipped with a storage 
battery, although it could be if desired. There is water 
enough to turn the wheel whenever the lights are necessary. 

Electric Lights from the Gasolene-Engine 

In figuring out the details of a small electric plant it is 
necessary to resort to Chinese methods and work backward. 
It will not do to begin with the generator. First make 
sure the exact purpose of the proposed plant. If it is to be 
used for electric lighting only, then we must first figure up 
the number of lights wanted and the number of hours they 
will be lighted each day. Make a list as shown in the following 


table. 

ROOM LAMPS LAMP-HOURS 

Kitchen. 1 6 

Living-room. 2 (lamps for 3hrs. = 1 lamp for 6) 

Dining-room. 2 3 yi 

Hall. 1 2 

Woodshed. I Lz 

Bedrooms (3). 3 (1 l am P eac h) 4 

Barn. 2 8 

Stable. 2 4 

Yard. 1 1 


Total. . 15 
263 


Total. .35 





















HARPER’S EVERY-DAY ELECTRICITY 


From this table it will be seen that the total illumination 
required per day is equivalent to burning one lamp for 35 
hours. In other words, to operate this plant we will need a 
storage battery capable of running one lamp for 35 hours 
or 35 lamps for one hour, or any other equivalent to this. 
In preparing the above table the lamps were all figured for 
maximum service, or the longest time they will be in use. 
In reality they will be used less than half of this, except when 
there is company in the house or in case of entertainment. 
But it would not do to put in lamps for ordinary service 
only. There must be enough power for emergencies. 

The Storage Battery 

If this plant is to be used for lighting purposes only a 
low-voltage plant with a storage battery will be best and 
cheapest. Storage batteries are rated in ampere-hours. An 
ordinary metal-filament 20-candle-power 20-volt lamp re¬ 
quires a flow of about one ampere at 20 volts to make it 
burn brightly. To make this lamp burn for 37 hours will 
require a 40-ampere-hour storage battery. This will give 
enough, and a little to spare for line losses, etc. 

To secure the proper voltage for a 20-volt system several 
things have to be taken into consideration. There is a con¬ 
siderable loss of pressure, or voltage, in a low-voltage system 
of this kind. This is especially true where the power-house is 
located some distance from the house or barns. The farther 
the current is carried the greater this loss. In purchasing the 
battery this loss must be considered. 

Each battery cell will give from 1.8 to 2.5 volts. Fifteen 
cells will give an average of 30 volts. This is 10 volts more 
than the lamps require, but these 10 volts will be lost in 
transmission or can be taken care of by a suitable battery 
switch. 


264 





DIRECT-CURRENT GENERATOR AND FEEDER SWITCHBOARD 








HARPER’S EVERY-DAY ELECTRICITY 


The Generator 

Remember that only direct current can be stored. So a 
direct-current generator will have to be purchased. The 
size of generator necessary is easily figured. A storage bat¬ 
tery of 15 cells produces, when charged, 2.2 volts per cell, 
or 33 volts. This is more than enough to light the 20-volt 
lamps. But when the cells are only partially charged they 
give but 1.5 volts each, or 22.5 volts. In charging a battery 
the current from the generator must be powerful enough 
to overcome the force of the battery, or the process will be 
reversed and current will flow from the battery to the 
generator. To charge a 33-volt battery it will require a 
45-volt direct-current generator. Ordinarily a current of 
five amperes is sufficient to charge a 15-cell 40-ampere-hour 
battery. It can be charged quicker with a 9-ampere current. 
If amperes times the volts equal the watts, then 9x45=405 
watts, or nearly half a kilowatt. The nearest commercial- 
size generator is ^-kilowatt, or 500-watt, machine. This 
will be ample to charge the battery. 

It will require a two-horse-power gasolene-engine to drive 
the generator to capacity, as gasolene-engines seldom give 
quite as much power as they are rated. A very good one- 
horse-power engine might drive it, and then again it might 
not. A large gasolene-engine may be used if it is properly 
governed. Some of the best engines are throttle-governed 
so they will produce any amount of power as desired with 
great fuel economy. The gas-engine should have a large 
balance-wheel to insure a steady driving-power. 

Controlling the Current 

This little plant is controlled from a switchboard located 
near the generator. An adjustable resistance, or rheostat, 

266 


INSTALLING A SMALL ELECTRIC PLANT 


comes with the dynamo. With this the voltage of the 
dynamo can be controlled at will so the battery can be 
charged slowly or fast as desired. Two measuring-instru¬ 
ments are necessary, an ammeter, to measure the current 
that is being supplied the battery when charging, and a 
voltmeter, to measure the pressure, or voltage, of the gener¬ 
ator. This voltmeter is also arranged to measure the volt¬ 
age of the battery and the voltage supplied the lamps. 
The switchboard should also be equipped with an automatic 
circuit-breaker. The purpose of the circuit-breaker is to 
prevent any loss of energy in case there is no attendant at 
the plant when charging and the engine stops. If this should 
happen the breaker automatically cuts out the current which 
otherwise would flow from the battery back into the genera¬ 
tor, turning it into a motor, and driving the engine backward. 

Because the voltage of the battery varies, being higher 
when fully charged and lower when nearing discharge, a 
little switch is mounted on the board for cutting in and out 
the end battery cells." When the battery is fully charged, 
producing 2.2 volts, the two end cells are cut out, thus 
bringing the voltage down to 27 volts for the battery. 
When the battery becomes weaker and produces but 1.8 
volts per cell these end cells are cut in, bringing the total 
voltage back to normal. 

The voltmeter is used for three readings. It is switched 
to the battery, line, or generator with a simple plug-switch 
at the will of the operator. The location of switches, in¬ 
struments, etc., is best shown in the drawing of a small 
switchboard for this plant (Fig. 3). 

The Lamp Circuit 

The lamps can be operated directly from the generator by 
using a double-throw switch. Throwing this switch one 

267 


HARPER’S EVERY-DAY ELECTRICITY 


way puts the battery on the line, throwing it the other way 
cuts in the generator. The complete wiring plan for this 
plant is shown in Fig. 4. 

A typical layout for the engine-room is shown in Fig. 5. 

Wires from battery to switchboard and from the switch¬ 
board to the armature terminals and from the engine-room 
to the house should be large enough to carry a maximum 
current of eight amperes without serious loss. If this dis¬ 
tance is not more than 220 feet, No. 8 B. and S. gage copper 



Fig. 3 


wire, heavily insulated, should be used. These wires are 
carried directly to the service-box in the upper floor of the 
house. The current is distributed about the house on 
ordinary No. 14 wire for the various branch circuits. These 
branch circuits will not be asked to carry more than three 
amperes. 

It is better to build a separate fireproof, small concrete 
building to house the generator, engine, switchboard, etc. 

268 




























































INSTALLING A SMALL ELECTRIC PLANT 



The engine may be either stationary or portable. Since 
only a few lights will be burned at a time on all ordinary 
occasions, the battery will not have to be charged more than 
once or twice a week, and the engine may as well be pumping 
water or doing other chores about the premises. 

Reducing Cost to Actual Figures 

Battery cells cost about #4.80 apiece. At this rate 
fifteen cells would cost $72, and they will last for several 
years with very little care. 

The cost of the switchboard varies. A good marble 
board equipped with the best instruments will cost about 
$95. A slate board and cheaper instruments will lower the 
cost considerably. 


Fifteen-cell battery, 40-ampere-hour.. $ 72 

Slate switchboard and instruments, etc. 80 

Shunt-wound, 45-volt generator, >2 kilowatt. 65 

Fifteen lamps, metal filament, 25 watts, 20 volts. 4.50 

1,000 feet No. 14 wire. 12 

550 feet No. 8 wire. 25 

Porcelain cleats and tubes. 2 

Fifteen snap-switches. 4-80 

Fixtures: 

Living-room, 3 lights. 7 

Dining-room, 2 lights. 6 

All others, each $2, total for 8. 16 


Total. $294.30 

269 
































































































HARPER’S EVERY-DAY ELECTRICITY 


Cost of wiring buildings is omitted, it being assumed that 
any one capable of installing a plant of this size can do the 
wiring and all the other work necessary about setting up the 
plant. Full directions for setting up the engine, generator, 
and battery come with these devices when they are pur¬ 
chased from the manufacturer. 

While low-voltage motors are not standard, there is no 
reason why they cannot be made. Doubtless one could be 
found among the smaller manufacturers, or they would wind 
one for a slight increase in cost. 

The above figures are given for new material and of the 
best. If second-hand material is used the cost of the plant 
can be materially reduced. 

Cost of Operation 

A two-horse-power gasolene-engine will consume about 
five cents’ worth of gasolene an hour under full load. When 
running a ^-kilowatt generator direct about .7 horse¬ 
power is necessary at a cost of about two cents an hour. 
The cost of operation for a generator is practically nothing, 
except for lubricating-oil, if it is given proper care and 
attention. The storage battery requires no supplies except 
a little sulphuric acid occasionally. The positive plates 
ought to last four and one-half years and the negative 
plates nine years with good care. 

A Standard Voltage Plant 

If standard voltage is to be used the plant should be 
considerably larger, as more current will be used when 
motors and heating-devices are available. The greatest 
increase will be in the cost for a 55-cell battery at $4.80 a 
cell. The generator will also cost more, depending on its 


size. 


GLOSSARY OF TECHNICAL TERMS 


A 

Absorption Coefficient. Surfaces 
absorb, to a lesser or greater degree, 
light-rays which fall on them. The 
percentage absorbed is termed absorp¬ 
tion coefficient. 

A. C. Abbreviation for alternating 
current. 

Accumulator. Storage battery; 
because it accumulates, or stores, 
electricity. 

Air Gap. The air space between 
two conductors, or terminals. The 
resistance of dry air is about 20,000 
volts per inch. 

Alternating Current. That form 
of electric current of which the direc¬ 
tion of flow reverses a given number 
of times per second. 

Alternator. A generator which 
produces an alternating current. 

Ammeter. An instrument for 
measuring electric current. 

Ampere. Unit of current. It is 
the quantity of electricity which will 
flow through a resistance of one ohm 
under a potential of one volt. 

Ampere-hour. Quantity of elec¬ 
tricity passed when electricity flows 
at the rate of one ampere for one hour. 

Anode. The positive-terminal in a 
broken metallic circuit; the terminal 
connected to the carbon plate of a 
battery; opposed to cathode. 

Arc, Electric. When the current 
“arches" over an air gap, usually ac¬ 
companied by great heat and intense 
light. 

Arc-lamp. A lamp which utilizes 
the intense heat of the electric arc as a 
source of light. Generally used for 


street lighting and the illumination of 
large areas. 

Armature. That part of a dynamo 
or motor which carries the wires that 
are rotated in the magnetic field. 

Armature Coils. The coils of 
wire in an armature. 

Armature Core. The shaft, or 
soft-iron core, of the armature. 

Attraction, Magnetic. Magne¬ 
tism. The “pull" of a magnet, caused 
by the shortening of the lines of force. 

B 

Battery. A generator of electricity 
by the action of chemicals. The 
primary battery actually produces 
electricity; the storage battery merely 
stores it in the form of chemical 
energy. 

Blow-out. When a fuse burns. A 
fuse is said to “blow out" when it 
melts and opens a circuit as a safe¬ 
guard against dangerous currents. 

Branch Conductor. A parallel, 
or shunt, conductor. 

Brush. The collector on a dynamo 
or motor, which slides over the com¬ 
mutator, or collector-rings, and col¬ 
lects the current for the circuit. 

B. T. U. British thermal unit—- 
the unit for measuring heat. The 
amount of work required to heat one 
pound of water one degree. 

Bus-bars. The heavy copper bars 
of the switchboard to which the 
dynamo leads are connected and to 
which the outgoing lines, measuring- 
instruments, etc., are connected. 

Buzzer. An electric alarm similar 
to an electric bell, except that the 


271 


HARPER’S EVERY-DAY ELECTRICITY 


vibrating member makes a buzzing 
sound instead of ringing a bell. 

C 

Cable. A heavy conductor. A 
bundle of insulated conductors pro¬ 
tected with a rubber or lead covering. 

Candle-hour. Candle-hour rep¬ 
resents a definite quantity of light just 
as a watt-hour represents a quantity 
of energy. A source of io candle- 
power operated for 1.5 hours would 
produce a total of 15 candle-hours. 
If operated for four hours it would 
produce 40 candle-hours. 

Candle-power. A measure of the 
luminous intensity of a source of 
light. The light of a standard sperm 
candle. The standard is known as the 
international candle, and is common to 
Great Britain, France, and the United 
States. The German, or Hefner, unit, 
is 10 per cent, smaller than the inter¬ 
national candle. 

Candle-power per Square Foot. 

Represents usually the ratio of candle- 
power allotted per square foot of floor- 
space in approximating illumination 
values. 

Capacity, Electricity. Relative 
ability of a conductor, or system, to 
retain an electric charge. 

Carbon. A non-metallic element 
extensively used in batteries and in 
other electrical devices. 

Cathode. The negative pole, or 
electrode, of a galvanic battery; op¬ 
posed to anode. 

Cell, Battery. A single unit of a 
galvanic battery; a unit of the 
storage battery. 

Charge. The quantity of elec¬ 
tricity present on the surface of a body 
or conductor. 

Chemical Action. The action of 
the chemicals in a galvanic cell where¬ 
by a current of electricity is produced. 

Choking-coil. Coil of high self¬ 
inductance. 

Circuit. Path, or conductor, over 
which the electric current flows. The 
house wiring is divided into various 
circuits. Conducting-path for elec¬ 
tric current. 


Circuit-breaker. Apparatus for 
automatically opening a circuit. 

Circular Mil. The cross-section 
of a wire is measured in circular mils. 
The circular mil is a small circle hav¬ 
ing a diameter of 1-1,000 of an inch. 

Collector-rings. The copper rings 
on an alternating-current dynamo, or 
motor, which are connected to the 
armature wires and over which the 
brushes slide. 

Color. A ray of sunlight consists 
of numerous waves of different fre¬ 
quencies which, when so combined, 
produce the so-called white light. If 
a ray of such light is broken up by a 
glass prism the spectrum, showing 
different bands or colors of light, is 
produced. Different materials ap¬ 
pear to have different colors, owing to 
the fact that all but the color re¬ 
flected is absorbed. 

Commutator. A device for chang¬ 
ing the direction of electric currents. 

Condenser. Apparatus for stor¬ 
ing static electricity. 

Conduit. A protective covering 
for electric wires. 

Converter, Rotary. A mechan¬ 
ical device to change alternating cur¬ 
rent into direct current, or vice versa. 

Core. The soft-iron central part 
of an electromagnet, or armature. 

Current. The flow of electricity 
over a conductor. 

Cut-out. Appliance for removing 
any apparatus from a circuit. 

Cycle. Full period of alternation of 
an alternating-current circuit. From 
the generator through the circuit to 
the left, and from the generator 
through the circuit to the right, con¬ 
stitutes one cycle. 

D 

D. C. Abbreviation for direct 
current. 

Depolarizers. Chemical agents 
used to correct the polarizing of 
galvanic cells. Cells are said to be 
“polarized” when an excess of ni¬ 
trogen gas collects on the negative 
element and prevents a continuation 
of the chemical action. 


272 










GLOSSARY OF TECHNICAL TERMS 


Dielectric. A non-conductor. 

Dimmer. Resistance device for 
regulating the intensity of illumina¬ 
tion of electric incandescent lamps. 
Used largely in theaters. 

Direct Current. Current which 
flows continuously in one direction. 

Discharge. The equalization of 
potential difference; opposed to 
charge. 

Dry Cells. Really wet galvanic 
cells, but the liquid elements are in 
paste form so they will not flow. 

Dynamic Electricity. Electric¬ 
ity in motion; opposed to static 
electricity. 

E 

Eddy Currents. Foucault currents, 
commonly called “eddy currents,” 
because of a fancied likeness to “eddy” 
currents in a stream of water. 

Electric Bell. A small bell oper¬ 
ated by an electromagnet and a 
vibrator. 

Electric Furnace. A furnace 
which utilizes the intense heat pro¬ 
duced by electricity. 

Electrode. Terminal of an open 
electric circuit. 

Electrolysis. Separation of a 
chemical compound into its elements 
by the action of the electric current. 

Electrolyte. The chemical solu¬ 
tion in a battery. 

Electromagnet. A mass of iron 
which is magnetized by current 
through a coil of wire wound around 
the mass but insulated therefrom. 

Electromotive Force (E. M. F.). 
Potential difference which causes 
current to flow. 

Electroscope. Instrument for de¬ 
tecting the presence of an electric 
charge. 

E. M. F. Abbreviation for elec¬ 
tromotive force. 

F 

Farad. Unit of electric capacity. 

Faradic Current. Currents pro¬ 
duced by induction. 

Feeder. A lead from a central 
station to some center of distribution. 

18 


Field. The region of magnetic in¬ 
fluence between the poles of a magnet. 

Field-coil. A magnetic coil used 
to produce the magnetism in the 
field, or between the poles, in a 
generator, or motor. 

Field of Force. The space in the 
neighborhood of a magnet. Within 
the influence of magnetic rays. 

Filament. The fine wire in an 
incandescent lamp, now generally 
made of drawn tungsten wire. 

Flaming Arc. A type of arc- 
lamp in which the luminosity is in¬ 
tensified by using special mineralized 
electrodes. 

Flux. Flux of light pertains to the 
waves which are emitted or flow from 
a source of light, and represents out¬ 
put, quantity. 

Foot-candle. The unit of in¬ 
tensity of illumination. It is the 
illumination obtained in a surface one 
foot from a one-candle-power source; 
or, expressed otherwise, a foot-candle 
is the intensity of illumination pro¬ 
duced by a standard candle at a dis¬ 
tance of one foot, or by a 16-candle- 
power incandescent lamp when meas¬ 
ured in the direction at which it gives 
16 candle-power at a distance of 4 
feet, as the intensity of light varies 
inversely as the square of the distance. 

Foucault Currents. Correct name 
for “eddy currents”; stray currents 
of electricity usually produced by 
inductive influences. 

Frequency of an Alternating 
Current. Commonly expressed as 
the number of double reversals in 
direction in one second. A double 
reversal is called a cycle, so that 
frequency is expressed as cycles per 
second. A 60-cycle circuit indicates 
that 60 double reversals occur each 
second. 

Friction. The force opposed to 
mechanical motion; corresponds to 
resistance as opposed to electrical 
motion. 

Fuse. A short piece of conducting- 
material of low melting-point which 
is inserted in a circuit and which will 
melt and open the circuit when the 
current reaches a certain value. 


273 


HARPER’S EVERY-DAY ELECTRICITY 


G 

Galvanic Cell. A chemical gen¬ 
erator, or battery, named after Gal- 
vani, an Italian scientist, who dis¬ 
covered the battery. 

Galvanometer. Instrument for 
measuring current-strength. 

Generator. Rotating-machine for 
producing electric current; two classes 
—alternating and direct current ma¬ 
chine; many different types of each 
class. 

Gravity Cell. A zinc-and-copper 
galvanic cell which is kept from polar¬ 
izing by the force of gravity; copper 
sulphate, being heavier than the zinc 
sulphate, settles to the bottom of the 
cell; generally used for continuous 
current, such as telegraph work. 

Ground. A circuit is said to be 
“grounded” when one of the con¬ 
ductors is short-circuited to the earth. 

H 

Helix. A spiral coil of conductor 
wire. 

Horse-power. The unit of me¬ 
chanical power. The energy re¬ 
quired to raise 33,000 pounds one foot 
in one minute; 746 watts. 

Horseshoe - magnet. A type of 
magnet bent in U-shape to shorten the 
distance between the two poles. 

I 

Incandescent Lamp. An elec¬ 
tric lamp in which a filament of high 
resistance is inclosed in a vacuum 
globe and heated white-hot by the 
passage of the electric current. 

Inductance. The property of an 
electric circuit to transmit itself 
through space, due to the lines of 
force which are developed around the 
conductor. 

Insulator. Any substance im¬ 
pervious to the passage of electricity. 

Intrinsic Brilliancy. A measure 
of the brightness of the light-emitting 
surface. It is expressed as candle- 
power per square inch. 


J 

Joule. Unit for measuring heat. 
The amount of heat generated by one 
ampere flowing for one second through 
a resistance of one ohm. 

K 

Keeper. A bar of soft iron, cor¬ 
rectly called an “armature,” laid 
across the poles of a magnet to retain 
the magnetism. 

Kilowatt. One thousand watts. 
(See Watt.) 

Kilowatt-hour. One thousand 

watt-hours. 

L 

Leyden Jar. Form of condenser 
which will store static electricity. 

Lightning-arrester. Device which 
will permit the high-voltage lightning- 
current to pass to earth, but will not 
allow the low-voltage current of the 
line to escape. 

Line. Often used by workmen in 
place of circuit. 

Lines of Force. The invisible 
magnetic rays which surround every 
magnet and every conductor carrying 
a current of electricity. 

Load. Work! A generator is said 
to be at “peak-load” when producing 
its rated capacity of current. The 
“ load ” is the amount of work required. 

Lodestone. A natural magnet. 
Probably derived from “leading- 
stone.” 

Lumen. A unit by which the lu¬ 
minous radiation from a source is 
measured. 

Lumens, Effective. The number 
of lumens falling on a surface, divided 
by the area of the surface in square 
feet, will give the illumination in foot- 
candles; or the number of lumens 
falling upon a surface, divided by the 
area of that surface in square meters, 
will give the illumination on that 
surface in lux, or meter-candles. 

Lux. The illumination produced 
by one candle at a distance of one 
meter is called the lux. It is equal to 
one meter-candle. 


274 


GLOSSARY OF TECHNICAL TERMS 


M 

Magnet. A piece of steel polar¬ 
ized by electricity. 

Magnet-coil. The insulated coils 
of copper wire of an electromagnet. 

Magnetic Field. The flow of 
magnetic rays between the poles of 
a magnet or magnets. 

Magnetism. Theory has it that 
magnetism is caused by the polariza¬ 
tion of the molecules of iron or 
steel. 

Mean Horizontal Candle-power. 

The average candle-power given by a 
source in a horizontal plane through 
its center when it is held with its axis 
in a vertical position. 

Mean Lower Hemispherical 
Candle-power. The average candle- 
power given by a source below the 
horizontal plane through its center. 

Mean Spherical Candle-power. 
The average candle-power given by a 
source in all directions and is a 
measure of the total flux of light issu¬ 
ing from the source. 

Mean Upper Hemispherical 
Candle-power. The average candle- 
power given by a source above the 
horizontal plane through its center. 

Meter. Measure. The common 
types of electrical measuring-instru¬ 
ments are the voltmeter, the ammeter, 
and the wattmeter. 

Molecule. The smallest part of 
any material. A molecule is said to 
be composed of atoms of various 
materials. 

Motor. A device to change elec¬ 
trical energy back to mechanical 
energy. 

Motor-generator. Motor and gen¬ 
erator on the same shaft for changing 
alternating current to direct, and 
vice versa, or changing current of high 
voltage and low intensity to current 
of low voltage and high intensity, and 
vice versa. 

Multiple. Term expressing the 
connection of several pieces of electric 
apparatus in parallel with one an¬ 
other. 

Multiple Circuits. See Parallel 
Circuits. 


N 

Negative. Opposed to positive, 
usually signified by the minus (-) 
sign. 

Neutral Wire Central wire in a 
three-wire distribution system. 

Non-conductor. Not a conductor 
of electricity. 

North Pole. The positive (+) 
pole. Opposed to south pole. Named 
after the north magnetic pole of the 
earth. 

O 

Ohm. The common unit of elec¬ 
trical resistance. The resistance of a 
simple circuit determines the current 
which a given pressure will produce, 
and is numerically expressed in ohms 
as volts divided by amperes. If a 
pressure of 24 volts causes a current of 
4 amperes through an electrical con¬ 
ductor the resistance will be equal to 
24 divided by 4, or 6 ohms. 

Oscillate. To swing back and 
forth; to vibrate. 

Overload. More than rated ca¬ 
pacity. An electric generator, or 
motor, will carry a heavy “overload” 
for short periods. 

P 

Parallel Circuits. Two Or more 
conductors starting at a common 
point and ending at another common 
point. 

Plating. The process of coating 
metals by the action of electrolysis. 

Plugs. Terminals of a connecting 
cord which are pushed or “plugged” 
into a wall receptacle for connecting 
electric heating-devices. 

Polarization. The depriving of a 
voltaic cell of its proper electromotive 
force caused by gases which neutralize 
the chemical action. 

Pole. Terminal. A magnet is said 
to have a north ( + ) and a south (—) 
pole. 

Potential. The pressure, or volt¬ 
age, of an electric current; expressed 
in volts. 


275 


HARPER’S EVERY-DAY ELECTRICITY 


Power factor. The power factor 
of an alternating-current supply in¬ 
dicates the ratio of actual watts to ap¬ 
parent watts which may be delivered. 
The apparent watts are equal to the 
product of the volts and amperes, but, 
owing to possible “phase displace¬ 
ment,” the power delivered may be 
actually less than the apparent power. 
The power factor is usually expressed 
as a decimal fraction. If a pressure 
of io volts delivers 2 amperes at a 
power factor of .8 (or 8o per cent.) 
the apparent power is 20 watts, while 
the actual power is .8 times 20, or 
16 watts. 

Primary. First. A galvanic bat¬ 
tery is called a “primary” battery 
because it produces a current of elec¬ 
tricity. A storage battery is called a 
“secondary ” battery because it merely 
stores, or accumulates, electricity. 

Projector. Searchlight; so called 
because it projects a beam of light. 

Push-button. A device which au¬ 
tomatically opens an electric circuit, 
but arranged so it can 'be closed with a 
push of the finger. 

R 

Rectifier. A device for changing al¬ 
ternating current into direct current. 

Reflection Coefficient. Surfaces 
reflect, to a lesser or greater degree, 
depending upon their nature and the 
quality of light, light-rays which fall 
on them. The percentage is termed 
reflection coefficient. 

Reflection, Irregular. If a light- 
ray strikes a roughened surface, such 
as, for instance, blotting-paper, it is 
broken up into a number of compo¬ 
nent parts, and these parts are reflected 
in all directions, hence we say that the 
light is irregularly reflected. 

Reflection, Regular. Regular re¬ 
flection is based on the theory that the 
angle of incidence of a light-ray equals 
the angle of reflection, hence we state 
that when a light-ray strikes a polished 
surface it is regularly reflected at the 
same angle at which it is received. 

Relay. To pass on. A telegraph 
relay receives a weak current of elec¬ 


tricity and draws upon the local bat¬ 
teries for a strong current to pass the 
message on to the next relay station. 

Remote Control. Controlling elec¬ 
trical apparatus from a distance by the 
use of magnets, or motors, etc. 

Resistance. The quality of an 
electrical conductor by virtue of 
which it opposes an electric current. 
The unit of resistance is the ohm. 

Residual Magnetism. The mag¬ 
netism remaining in a soft-iron core 
when a current of electricity is not 
flowing in the magnetizing-coils. The 
magnetism that is left, or remains. 

Rheostat. Resistance device for 
regulating the amount of current. 

Rotary Converter. Machine for 
changing alternating current to direct 
current, or vice versa. 

Rotating-field. In some genera¬ 
tors and motors for various mechanical 
reasons the field is revolved around the 
armature instead of turning the arma¬ 
ture within the field. Obviously it 
makes no difference in the flow of cur¬ 
rent whether the field or the armature 
is revolved. 

S 

Secondary Battery. See Storage 

Battery. A battery whose positive 
and negative electrodes are deposited 
by current from a separate source of 
electricity. 

Secondary Current. The current 

induced in the secondary winding of 
an induction-coil or transformer. 

Self-inductance. Tendency of 
current in a single circuit to react 
upon itself and produce a retarding 
effect similar to inertia in matter. 

Series. Arranged in succession, as 
opposed to parallel or multiple ar¬ 
rangement. 

Series Motor. Motor whose field- 
windings are in series with the 
armature. 

Short Circuit. When the circuit is 
suddenly shortened by the current es¬ 
caping through the ground or over 
another conductor. 

Shunt. A by-path in a circuit 
which is in parallel with the main 
circuit. 


276 


GLOSSARY OF TECHNICAL TERMS 


Shunt Motor. Motor whose field- 
windings are in parallel or shunt with 
the armature. 

Single Phase. A current of one 
phase, or value. 

Snap-switch. A small wall-switch 
used to snap on and off the current. 

Solenoid. An electrical conductor 
wound in a spiral and forming an 
electromagnet. 

Spark-gap. Space between the 
two electrodes. 

Starting-box. A rheostat, or re¬ 
sistance-box; generally used in start¬ 
ing motors to lower the initial voltage 
until the machine is running at full 
speed. 

Static Electricity. A high-poten¬ 
tial stationary charge of electricity 
which may exist on insulated bodies; 
produced by friction; lightning is a 
form of static electricity. 

Stator. The stationary part of an 
alternating-current generator or motor. 

Storage Battery. A device de¬ 
signed for the storage of electrical 
energy by chemical means. 

Switch. A device to open and 
close a circuit. ' 

Switchboard. A board, or panel, 
of wood or stone, to hold the switches, 
instruments, etc., for controlling the 
distribution of the current. 

Synchronize. To be in step, in 
balance; to work in harmony. 

T 

Terminal. The end of an open 
circuit. 

Thermostat. Instrument which, 
when heated, closes or opens an 
electric current. 

Three Phase. An alternating cur¬ 
rent with three different phases, or 
values. 

Three-wire System. Where three 
wires, or conductors, are used to dis¬ 
tribute the electric current. 

Transformer. A device for step¬ 
ping-up alternating current from low 
to high voltage, or vice versa. 


Transmission. The distribution 
of electricity over wires, or conductors, 
often for hundreds of miles. 

Trolley. A device for connecting a 
trolley-car with the overhead trolley- 
wire. 

Turbo - generator. A generator 
directly connected to a steam-turbine 
engine. 

Two Phase. An alternating cur¬ 
rent of two phases, or values. 

V 

Vibrator. A spring device used to 
“make” and “break” an electric 
current. Necessary for direct current 
only. 

Volt. Unit of electromotive force, 
or potential. It is the electromotive 
force which, if steadily applied to a 
conductor whose resistance is one ohm, 
will produce a current of one ampere. 

Voltage. Potential difference, or 
electromotive force. 

Voltmeter. Instrument for meas¬ 
uring voltage. 

W 

Watt. Unit representing the rate 
of work of electrical energy. It is the 
rate of work of one ampere under a 
potential of one volt. Seven hundred 
and forty-six watts represent one 
horse-power. 

Watt-hour. Electrical unit of 
work. Represents work done by one 
watt expended for one hour. 

Watts per Candle. Indicate the 
amount of electrical power necessary 
to produce unit luminous intensity. 
When rating incandescent lamps of 
specific consumption yi watts per 
candle is usually based on the mean 
horizontal candle-power. 

Watts per Square Foot. Repre¬ 
sents usually the consumption allotted 
per square foot of floor-space in ap¬ 
proximating illumination values. 

Wiring. The wires installed for an 
electric circuit, 









INDEX 


A 

Alternation, 193. 

Alternator, 179. 

Ammeter, 196, 199. 

Ampere, 7, 148. 

Arc-lamp, 72. 

Armature, 185, 186, 187, 219, 221, 225, 
226. 

to wind, 186. 

Attraction and repulsion, 72. 

B 

Battery, action of, 2. 
circuits, 14, 15. 
closed circuits, 9. 
current, 6. 
defect, 3. 
dry cell, 9. 

gravity type, 4, 11, 12. 
lighting, 43, 44, 45, 46. 
open-circuit, 10. 
primary, 2, 5. 
secondary, 2, 56. 
signal systems, 39, 40, 41, 42. 
storage, 54, 55, 56, 57, 62, 63, 264. 
Bells, electric, 28, 29, 34. 
Burglar-alarms, 30, 36, 37, 38. 

Buzzer, 15, 26, 32, 33, 34. 
signal systems, 32. 

c 

Candle-power, 121, 122. 

Circuit, battery, 19, 22. 
branch, 92. 

electric as compared to water, 75, 
76, 192. 
lamp, 267. 

metallic, 19, 77, 78, 267. 
three-wire, 77. 
two-wire, 77, 


Circular mil, 79, 80. 

Coal, energy of, 69, 70. 

Code, Morse, 33. 

Coil, induction, 173. 
primary, 234, 241. 
secondary, 234, 241. 
Commutator, 177, 187, 188, 221. 
Conductor, 78, 79, 80. 

Cooking by electricity, 155, 156. 
Current, alternating, 191, 192. 
control, 97. 
direct, 191, 192. 

D 

Detector, 173. 

Drop-light, 136. 

Dynamo, discovery of, 171. 
experimental, 175. 

E 

Electrodes, 2. 

Electrolyte, 5. 

Electromagnet, to make, 29, 184. 
Electromotive force, 4, 14, 148. 
E. M. F. of various batteries, 9. 
Energy explained, 1, 7. 
transmission, 235. 

F 

Fans, electric, 212. 

Farm, electricity for, 251, 253. 
Field, magnetic, 188. 

Fire-alarms, 40. 

Force, 7. 

Frequency, 193. 

Friction, 8, 145. 

Fuse, 24, 25, 9°> 9 1 * 

G 

Galvanometer, 173. 

Geissler tubes, 233, 





HARPER’S EVERY-DAY ELECTRICITY 


Generator, 169, 189, 227. 

alternating current, 178, 179, 190. 
direct current, 177. 
how to make, 181, 183, 184, 185. 
kinds of, 178. 

H 

Heat, electric, 150, 151, 152, 153. 
experimental, 134, 157, 158, 159. 
how produced, 152, 157. 
Heating-circuit, 153. 

Heating-units, 153. 

Horse-power, 147. 

I 

Incubator, electric, 159. 

Induction, discovery of, 169, 172, 173, 
230. 

theory, 171, 232. 

Induction-coil, 173. 
experiments, 229. 
to make, 232. 

Insulator, 106, 107. 

K 

Key-sockets, 98, 101. 

L 

Lamps, arc, 72. 

experimental, 132, 133. 
flash, 52. 

incandescent, 128, 129. 
miniature, 45, 46, 50, 53, 144. 
proper location, 116. 

Light, absorbed, 113. 
color values, 115. 
electric, hi. 

shades and reflectors, hi, 113, 117. 
Lighting, adaptations, 135, 136, 137. 
cost of, 118, 121. 
explained, 72, 109, 112. 
house, 124, 125, 126. 
motor-boat, 49 
Light-waves, 114, 130. 

Lines of force, 170, 206. 

M 

Magnet, horseshoe, 172. 

to make, 181. 

Magnetic field, 206. 


Magnetism, 170, 171, 207. 

Magneto, 183. 

Measuring electricity, 196. 

Mercury-arc rectifier, 61. 

Mil-foot, 80. 

Motor, explained, 205, 208. 
alternating-current, 210. 
direct-current, 208. 
experimental, 218. 
household, 213, 216, 289. 
Motor-generator set, 60. 

N 

Non-conductor, 105, 106. 

O 

Ohm, 7, 148. 

P 

Phase, 193, 194- 
Plant, private, 246, 260. 
cost figures, 269. 
essentials of, 247. 

Polarize, 3. 

Poles, magnetic, 171. 

Potential, 7, 148. 

Pulleys, speed of, 190. 

Push-button, 23. 

R 

Radiator, electric, 165. 

Rays, magnetic, 169. 

Reflection of light, 113. 

Repulsion, opposed to attraction, 172. 
Resistance, 7, 15, 80, 81, 82, 83, 145, 
146, 147, 150. 
box, 239. 
wire, 151. 

Rheostat, 239. 

Rotary converter, 59. 

Rotor, 179. 

S 

Series conductors, 16. 

parallel, 17. 

Shades, lamp, 137. 

Shunt circuit, 189. 

Soldering-iron, electric, 160. 

Stator, 179. 

Street-cars, explained, 73. 

Switch, 21, 22, 100, 101, 102, 103, 104, 
105. 


280 



INDEX 


Switchboard, 265, 266. 

Switch, wall, ior. 
master, 105. 
two-way, 104. 
three-way, 104. 

Symbols, 81, 93, 94. 

T 

Toaster, electric, 163. 
Transformer, 234, 237. 

small, 241, 242. 
Transmission wire, 235. 

Turbine, steam, 67, 68, 69. 

V 

Vibrator for induction-coil, 233. 
Volt, definition of, 7, 15, 148. 


Voltage, 14, 81, 148, 270. 
Voltmeter, 197. 

W 

Water-power, 254. 
plant, 262. 

Watt, definition of, 7, 148. 
Watt-hour, 120. 

Wattmeter, 198, 200, 202. 
Waves, light, 115. 

Weir, 256. 

Wind, power of, 258. 
Windmill electric plant, 261. 
Wire, carrying-capacity, 82. 
Wiring, cable, 88. 
indoor, 84. 
knob and tube, 86. 
molding, 85. 
service wires, 89. 


THE END 



























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